A tried, tested and maybe tired trope today, a possible entrance to a secret passage.
a large drop
easily overlooked / a weakened/damaged
This is less suited to wargaming than recent Triffles, but if a trapdoor is included as part of a terrain piece - as the entrance to yesterday's passage perhaps - it makes sense to consider that drop: does it only slow movement or potentially cause injury?
Roleplayers might be more interested in whether or not the trapdoor can actually be found. It could be most easily overlooked if high, especially in vaulting, or possibly concealed by an object if low. If underfoot with a weakened/damaged structure, it would be best to find it sooner rather than later.
For all, the key question might be of what's on the other side, especially if the space is dark, and writers may need to consider how we feel about this unknown. Often, in fiction, there's something down (or up) there...