The regular trapdoor is opened by flipping a Lever/Switch, using a Key or sometimes by simply triggering it by stepping on it. There are also two special kinds of trapdoors that can be opened without any special gear, the Ceiling Trapdoor and the Floor Trapdoor, both introduced in Tomb Raider IV: The Last Revelation.
When a trapdoor opens after using a key or another kind of trigger, you hear a distinctive sound.
Tomb Raider II
The trapdoor returns in Tomb Raider II, in the first level The Great Wall, inside the first tower of the wall. Here the trapdoor is triggered automatically; when Lara steps on it, it sends her down into a pool of water. In Venice you will encounter a set of trapdoors that are linked to the same Small Push Switch and function like a double door system. Another trapdoor is found in Bartoli's Hideout, after obtaining the Library Key and performing some Chandelier acrobatics during which you will open the trapdoor using a Wall Lever (also known as Big Lever Switch). Another trapdoor is found in the Opera House level. It is in the roof, behind a Swinging Crates and is opened by throwing a Small Lever Switch. The second trapdoor in the Opera House is special. It is not opened by a lever but by a Falling Sandbag crashing through it. [...] In the level Barkhang Monastery Lara is tasked with finding a Trapdoor Key that opens a trapdoor that leads to an outside location where one of the Prayer Wheels is found.
Tomb Raider III
- A trapdoor in the ceiling that can be opened by jumping up towards the handle while standing underneath looking inwards.
- A trapdoor in the floor that can be opened by standing in front of the handle and lifting it up.