Yeah, I hadn't actually used traps or pressure plates, only levers.
For instance, there are two levers, one inside a tower and one outside. The tower is blocked by a floodgate. By hitting the outside lever, the floodgate opens, but a pump turns on outside, flooding another area that the player doesn't know of yet, but the idea is that he notices the pump suddenly doing something. The inside lever, however, is only connected to the pump. By pulling it once, nothing happens, and the player might think that's all that needs to be done. But, if it were pulled again, the pump would turn off, and tada! Wherever you were going to go next won't be flooded and impossible to get through (or at least easily).
I also had a large room that had one ledge you stand on, and another farther away. Reaching the other edge is impossible due to a large pit in the center. However, there is a lever that activates a pump, flooding the pit. Once its full enough, the player can simply swim to the other side. The problem is that it requires timing, as the channel from the pump to the room is very long, so even after the pump is off, there is still a long channel full of water draining into the room.
But that might not be a bad thing. The room after the pit has a series of bridges and floodgates, and many levers connected to them. Having all bridges down and floodgates up is impossible, but if the pit room floods enough... it will leak into the bridge and floodgate room, allowing the player to swim across, assuming all the floodgates were up. Most players won't see the easy solution and will continue pulling levers for a good while :p. It also has one inconspicuous lever that secretly turns on another pump that floods yet another room unknown to the player, possibly waiting further in. Yeah, less skill and more luck, but oh well, losing is fun?
[ May 26, 2008: Message edited by: Vaiolis ]