Barnabus (on the central platform in the main cave, with the forcefield around it), is part of the Hunting We Shall Go Again quest, as well as one of Igor's quests, if you choose him as a necromancer. A dragon skill book is available once you disable the two generators powering the forcefield, and you probably already got the skill book in the chest near the Book of the Dead.
There are no platforms or jumping in D:OS.
For the the platforms in the bottom of the three teleporters:
- jump up the first series of platforms until you get to the stationary ones
- jump to the moving platform to get to the first lever that activates the teleporter below
- drop down, careful of where you'll land, and take the teleporter to one up higher
- make your way across the moving platforms
- take the ladder up, and make your way back to the other side with a couple moving platforms, and one that starts dropping when you land on it (just down one level, if you stay too long)
- loot the chest and take the top teleporter... that will put you on the opposite side of the area (right at the T intersection)
- jump down to the platform in the corner to the right, when facing away from the teleporter
- jump down another couple platforms, and there will be a lever to disable a generator and get a platform moving back and forth below at 'ground' level
- drop onto the moving platform, timed so you hit it rather than the lava, then jump onto the stairs when you are close enough, and you are done with that section
