The Ancient Tool was a staff-like object with a pearl on the bottom tip that could be used to activate machinery when inserted into clam-like sockets. One was in the posession of Marquis De Singe, who used it to access the power of the Vaycaylian wind control idol, as well as the giant door that led to it. Guybrush aquired it when he used his pyraite parrot to scare de signe who would drop it. Guybrush would then use the tool to activate the different idols and thus cancel the majical winds preventing him and everyone else from leaving the island.
The human Lechuck also found another one on Spoon Isle that lacked its pearl part. Guybrush helped give his former nesisis the missing part and together activated the machine to open the stone chest containing the golden turtle artefact.