Crypts of Durkon Overview - Baldur's Gate 2
The Crypts of Durkon is a map that is involved in Hexxat's Companion Quest; you will only gain access to this area for a very brief time while you're doing this quest. How it works is someone named Cabrina will approach you 1 week after Hexxat joins your party and give you the task that unlocks this crypt. To reach this crypt all you need to do is visit the Graveyard District and tell Hexxat that you're ready to travel here.
Your goal inside this crypt is going to be defeat Nan Kung Chi in the northwestern section and loot The Claw of the Black Leopard from the tomb right next to him. There are numerous ways to solve this quest, most of which I talk about on the Hexxat's Companion Quest walkthrough and below on this page. I recommend you explore this map thoroughly too as there is quite a bit of loot to be found throughout the sarcophagi in this area.
Keno Ghost: Keno will ask for help if you don't antagonize a fight with him. Helping him will require you to defeat some Umber Hulk and Mind Flayer enemies in the northern part of this tomb. Regardless of your choice to attack or help him you'll end up with the Key of Scholars either way which we need to enter the second half of this tomb.
Ki Chin Sang: This NPC holds the Key of the Master's Crypt which you can take from him by force, through pick pocketing or by proving your worth to him. If you choose to prove your worth you'll have to fight 6 different named enemies in the room just south of this NPC. Attack any of the sarcophagi in the room to the south to make all 6 enemies appear; defeat them then talk to Sang again to get the key.
Nan Kung Chi: Nan Kung Chi is a named mummy who is the head honcho of this tomb. You have no choice but to fight him but thankfully it's not a difficult fight. You'll find The Claw of the Black Leopard in the tomb next to where Nan Kung Chi was found. Looting this item will complete this map.