A hole is part of a transportation mechanic in the Underwater Agility and Thieving training activity, which is located in the Underwater area of Fossil Island. There is a total of ten holes. Players can enter a hole, which will bring the player to one of the other holes in the area.
Entering a hole will reward the player with 4.5 Agility experience.
The destination each hole links to is fixed. See the image below for an overview of linked holes.
A map of the underwater area, with holes having matching colours to help navigate.