An antipattern.
A potential, unsuspected, hidden problem, hazard, or danger that is easily encountered but not immediately obvious.
A type of trap consisting of a concealed pit in the ground, which the victim is supposed to fall into and not be able to get out from.
Subsidence below ground in a mine, which can cause the ground level above to drop.
Something that disrupts smooth operation or functioning; used especially in phrases such as throw a spanner in the works, put a spanner in the works etc.