Netherstorm Citadel is one of the two dungeons made out of bedrock. The entrance is a narrow stone bridge, leading to a wider wooden bridge. Rooms inside consist of libraries, lava rooms, a room with lapis walls and stairwells. Under the citadel is where the black wool is located, guarded by what used to be skeleton turrets but are now Wither Skeletons stuck in cobwebs and a Ghost mob called a Char.
Points of Interest
16 diamonds along with bedrock (to be used with care)
Fun box encased (except of one-block-height stone wall) in bedrock right next to the fleecy box
Parkour section above lava.
The hole leading to the fleecy box also leads to the void.
Lava hidden in gravel can be avoided by building above the gravel
Although dispenser in the front wall can shoot you they also allow you to make a breach in the wall - you can avoid going throughout the courtyard.
Also to avoid fighting endless army of spiders and witches you can build around the courtyard from top of the wall (at the opposite side of the entrance there is a platform blocked only by some fences - a path further into the dungeon is there)
Parkour section can be completely avoided by simply building a bridge.
On the left side of the staircase after the parkour is a hole from which zombie falls from above - block it and now you only need to get to the top of the stairs and destroy the spawners.
Road to the chest with diamonds is quite easy - just bring some building blocks and destroy spawners on the way (2 of them - one near to the chest and 2nd under the stairs in room with lapis walls.
Second room before the fleecy box contains skeleton spawners inside bedrock surrounded by cobwebs - almost all skeletons and chars from the next room will get stuck inside of them. Build over the bedrock containing skeleton spawners and build a bridge to the platform with char spawner. Then block the way for spiders from below the same platform and destroy ghast spawners. After that clear the area of all skeletons and chars.
Mobs from the fun box are blocked by a small pit - they will accumulate there - use creeper or tnt explosion to kill them and get to the fun box before mobs spawn again. Light whole area or destroy the stone at the back wall of the fun box, put tnt inside and blow it up.