Trapdoors, Drawbridges, Portcullis, Pulleys, Cranes
Functional trapdoors, drawbridges, portcullises and pulleys for raising/lowering platforms would be incredible - each should have the ability to open/close or 'lock' them in place so a drawbridge could be raised 30% or a pulley could lift a platform 55% etc. and be locked in place. Cranes for lifting things that have pivoting arms etc would be awesome too.