Detonator Key
From WikiRaider
The Detonator Key is found in Bartoli's Hideout in Tomb Raider 2.
It is found on a small platform in a shack, guarded by a Fiamma Nera
Once inserted into it's receptacle on the floor in another part of the outdoor area, the hideout explodes, allowing Lara to get to the level exit behind the now destroyed building.