The barrel of salt is in the kitchen on the second level of the citadel (
map), where there are 4 soldiers waiting outside and the cook asks you to find an imp.
The key to open the door to the room with the stairs to act 2 can be found in one of the 2 rooms off of Samuel's lair (that is also where you will find the level 3 BF key).
There should be 3 levels to all BF dungeons.
Sometimes an entrance can be partly or completely obscured by a wall. Check the auto map, to see if you can see some blue sticking out somewhere. Running around methodically searching with the mouse can also help.
Occasionally the entrance can be a pile of rocks, rather than the usual fountain thingy.
Rarely part of a level can be separated from the rest, which could contain the entrance to the next level. Check your map, and see if it looks like there may be more to the level than you have explored.
