Note: I used a mod when i made this. (the laser mod) but it can still be done without it.
Purpose: to help defend the door to a castle.How: when bridge is off, it retreats under a moat of lava
I used 14 laser emitters (2 as the in-castle switch) 4 reflectors, 12 sensors, 12 sticky pistons, 12 cobblestone, and 12-14 redstone wire. The castle this protects was generated by more creeps and weirdos mod, but my laser messed up the more creeps mod, so i just went with it.
Please leave questions below this text. I am going to start a SMP clan. Webpage coming soon.
Do you have a layout plan or video showing you constructing it so we can easily replicate your design?
The wood lies directly over the lava. It won't catch fire when shut, so if it does catch fire just shut it. Also it is possible to ide the redstone. The lever is the only part that you can see when everything is hidden.Note: You might want to close the bridge after someone falls in because there is a chance they might be able to get out. When it is closed the suffocate also. The way I did it no mod is needed or used only redstone sticky pistons, your walkway, and something to cover the pistons/redstone.