The Undead Crypt can be accessed via the Shrine of Amana after defeating the Demon of Song boss. When you enter the crypt after descending the lift, the first room you should arrive at will have a staircase leading up in front of you. Underneath the stairs (head to the left side to access it) is the first bonfire of the area. On the other side of the stairs is a skeleton holding a Radiant Life Gem. Head up the stairs and follow the short hallway beyond to reach a new room with light shining through the doorways ahead, The source is a torch wielding hollow that needs to be taken down as quickly as possible. The reason why is that a nearby NPC will become hostile if the torch hollow follows you further in and gets too close (make sure you are not carrying a torch either when the voice warns you shortly as that will also make the NPC turn hostile). Into the next room from where the torch zombie was cautiously as two hollows and three leydia witches are present in there. The leydia witches can use a variety of spells, pyromancies, miracles and hexes. Equip as much magic and elemental defense as you can before engaging them as they can tear through health if you have insufficient defenses (especially their lightning spear and firestorm spells). Once the room is clear, head into the nearby hallway. Make sure you have no torch up from this point forward until you are well past the NPC.
When you emerge out of the hallway into the next room a voice will tell you to not produce light. The NPC who warns you is named Agdayne and can be found on the ledge above to your right along with his troops. They, like him will not become hostile unless they are attacked directly or a torch is lit. To reach him, head up the stairs on the right side of the room and walk past his warriors to talk the hollow leaning against the wall at the back. This is Agdayne. He teaches the have mercy gesture as well as selling some equipment and some higher end spells. You can also talk to him to find out some interesting story tidbits. You can return to Agdayne after defeating Vendrick (optional endgame boss) to receive the Darkdrift Katana and his armour set. To the right of Agdayne is a corpse hanging over the ledge that holds a Large Soul of a Nameless Soldier. Descend the stairs and head out the other door into another short hallway with light at the end. When you emerge, you will see a bridge to your right with two Royal Knights on it. These act just like the syan knights from Drangleic Castle (and nearly any enemy with a shield), after being hit once they will put up their shield and approach you until they are within striking range and then attack. After the attack is your window of opportunity to damage them, no matter what character type you are. Lure them down one at a time and kill them both off.
The door you just came through has a platform below it that you can drop down to. Be careful when you do though as two hollows will be waiting below. A skeleton holding Simpleton's Spice and the Soul of a Great Hero will be on the lower platform as well. Ascend the ladder at the far end of the platform to reach a level above the bridge with a hollow standing nearby. Take care of him and open the chest he was guarding to pick up a Crushed Eye Orb and a Fire Seed. From here, you can drop back down to the bridge for a tiny bit of fall damage. Cross the bridge and walk past the mist door on the other side. At the end of this platform you can drop down as well to a lower platform (we'll be coming back to that mist door from the other side). You can light the woman statue at the bottom of the steps here to light part of the area. Enter the doorway here and open the chest to find a Soul Vessel. A nearby ladder leads up to a skeleton holding the Soul of a Hero. Walk over to the next ladder nearby and descend to the bonfire below.
The next room contains a large amount of tombstones that infinitely spawn hollows and statues that generate specters until the statues are destroyed. Specters are fast, can travel through the tombstones and wield powerful pyromancies and sorceries as well as using lunging weapon strikes. Your first task in the room is to find and destroy each of the three statues in the room. Melee attacks work best (even hitting it with a staff was more effective than lobbing lightning spears at it in my case). Thankfully the statues will not respawn once broken, even if you die or teleport. Two corpses can also be found in this room that hold: Simpleton's Spice, Black Firebombs, a Titanite Chunk and Petrified Dragon Bone. Once you are done, look for a ladder near the large door with two torches (in the corner) and climb up to engage a leydia witch (ranged characters can ignore the ladder for now and enter the next room if they find this head on confrontation in a small area too difficult). Melee characters will be able to rush her and take her out easily. Open the chest behind where she was standing to obtain Dried Fingers, a Bonfire Ascetic and Twinkling Titanite.
Climb back down the ladder and head through the door on the opposite side of the room to the bonfire (this next room is filled with tombstones and statues as well). When you enter, go to work on the statue to your left as quickly as you can. There is another one to the right in a small alcove in the wall, but of more immediate concern is a Leydia Witch on a platform above you to the right (if you didn't just take her out) when you enter the room who will start casting immediately. Destroying the statue near the door prevents specter back attacks. If you have ranged attacks, you can dodge in and out of the entryway taking potshots (keeping an eye out for the spawning hollows of course). Remember to go back to the ladder in the previous room to climb it and open the chest she was guarding if you didn't kill her earlier. Pick up the Soul of a Lost Undead from the corpse at the base of the stairs and a Bracing Knuckle Ring +2 from the body in the corner behind the second statue.
When the room is clear (apart from the infinite hollows), head up the nearby stairs and walk into the room to be invaded by the Nameless Usurper phantom again (he appeared in Drangleic Castle just before the twin dragonrider fight). He is just the same as last time, so used ranged attacks if you have them. Melee characters will be able to easily block or have longer reach than him with larger weapons so taking him down shouldn't be too hard. Beware getting too close to the walls in this room as wall ghosts with swords will emerge from them and physically attack you if you get close, possibly stunning you and letting enemies get free hits on you. After defeating the phantom, loot the nearby corpse for a Divine Blessing and Soul of a Hero. There is a hidden door in this room as well (to the right as you entered this room). Two wall ghosts are inside, guarding the chest that contains Avelyn and Heavy Bolts. Return to the previous room and take the opposite door into a curving hallway that opens up and leads three wall ghosts and two Greatshield Royal Knights. These knights dual wield the shields and can deal annoying amounts of damage with their shield bash attacks while only being very vulnerable when they attack. All characters should bait their attacks and then counter attack after evading it. At the end of the hall is a large hole in the floor. Heal up and make sure you are prepared before dropping down as this is a dangerous area and it is annoying to trek back from the bonfire.
Assuming you dropped down from the side of the hole closest to the hallway, let me lay out the four paths out of the room. The door behind you when you fall contains a hollow that will ring a bell that summons infinite specters from the statues in the room while the bell is ringing (and the hollow only stops ringing the bell when you kill it). The door to your right when you drop down contains a statue that spawns specters (needless to say this should be destroyed). The passage to the left when you drop down (has a groove in the floor) is the way out of here. The door directly opposite when you drop down is a short tunnel with a corpse at the end with a Large Soul of a Proud Knight and Dragon Charm on it. There is also a hidden door in the same wall that contains a pharro's device that lights up a hidden door on the opposite wall. Attack the symbol to open the door and open the chest inside to pick up Olenford's Staff and the Great Lightning Spear miracle. There are a total of four specter statues in this room (including the one in the nearby passage) and two summoning bells (one in the main room and one in the nearby passage). Destroy all the statues to prevent specters spawning and pick up the items (a skeleton in the center of the room holds a Radiant Life Gem and a Homeward Bone to grab) before moving on down the passage with the groove in the floor.
Head left as soon as you emerge from the hallway to find a lever that lowers a bridge that acts as a shortcut to the bonfire. This allows you to quickly travel through the first tombstone room and head straight here. Return to where you entered this room and straight ahead to find a chest containing a Magic Stone and a Darknight Stone. The large doorway leading to a huge hall is your next destination (and the mist door at the other end leads to the area boss). Before entering the room let's explain how it works (and why this is important). This spot is a great place to grind as it has an infinite amount of specter enemies. A hollow underneath the staircase rings the bell, summoning specters infinitely. They don't move until they are attacked or you get very close so they are quite easy to kill with ranged attacks. You can kill the specters over and over again as they do not have a respawn count (they are summoned, not set enemies). As long as you don't kill the hollow under the stairs fifteen times, you can grind here indefinitely.
At the other end of the hall (past the specters) are seven royal knights with swords and shields. You can sprint along the sides of the room and dodge through the knights if you just want to fight the boss. Get to the mist door in whichever way suits you and enter it to face the area boss.
Boss: Velstadt, The Royal Aegis
Personal Death Count: 0
Horizontal Swing: Velstadt pulls his hammer behind him and then swings it in a large arc in front of him. Roll backwards to avoid the attack.
Overhead Swing: Velstadt will raise his hammer overhead and then sprint towards you before swinging it down into the ground at your position. Roll to the side to avoid this predictable attack. It does do a fair bit of damage if it connects though.
Dark Orbs: Velstadt will charge his power of darkness (staying stationary) and then fire dark orbs towards you. Roll or sprint to the side to avoid them.
When you enter the mist, Velstadt will be waiting within (what is this? the seventh boss that is just a dude in armour?). He is the King's personal body guard and wields a giant hammer. He will start the battle by performing simple melee attacks that are relatively easy to dodge. Just be careful to not be pinned against a pillar and you should be able to roll away with ease. Bait his single swing attacks and then get some damage in during his long recovery animations. Ranged characters will be able to just constantly back up and pummel him.
When he drops below fifty percent health, he will kneel on the ground and be surrounded by a glowing dark aura. This means he is now able to cast dark magic spells and will occasionally do so in between his melee attacks. The advantage to this is while he is kneeling and getting up you can hammer the hell out of him, downing him very quickly. If he manages to get up, just resume the above tactics until he falls. Overall he is a very easy boss.
Once the boss is defeated, the mist door at the other end of the room will disperse. This will lead to a large circular area with the King (Vendrick) almost naked except for a loincloth and huge sword patrolling the area. He will not attack unless attacked multiple times and you will probably want to save battling him for after you finish the story, His defenses start at a multiplier of 32 and are halved with each Soul of a Giant you have in your possession. At this point you most likely only have one at most, making him 16x tougher than normal. If you really must attempt him now, grab the King's Ring (key item: opens king's doors scattered around the world) first. You can find the strategy for dealing with this boss in the endgame content section of the guide. For those not suicidal, just grab the King's Ring and head back to the bonfire to continue the journey in Aldia's Keep, the next destination we need to head to.