Some say that Kharos is the hardest place that exists in the game, besides the Pits of Inferno.
Those without a very high level might die instantly if they were to enter.
This tower is filled with all sorts of terrible creatures, including many Liches, Serpent Spawns, Warlocks, Dragon Lords, Behemoths and Demons.
The tower was sealed off by the Edron magic academy. To access the tower, talk to NPC Zoltan in Edron and ask for "permission". He will let you enter by paying 500 gps (note that if you paid once and entered there, you have to pay again).
Warning! When you step into the citadel, you will be greeted by several behemoths, and possibly lured demons and dragon lords. If you are low level (lower than about 150), you are advised to not move at all until everything around you is dead. Stay at the wall so "only" 5 creatures can reach you. If you are high level, you can run north-east to the basement stairs.