Sub Brit member Tim Wellburn will outline the development of Gibraltar's labyrinth of tunnels, constructed from the late 18th century up to the 1960s. By far the most intensive period of tunnelling took place during WWII when the Royal Engineers excavated 18 miles of underground facilities designed to allow the garrison to withstand a one-year siege.

He will then illustrate a walk through the length of the northern tunnels, mostly dating from this period. Entering the system approximately half-way down the peninsula, his route takes in communications, power generation, medical, storage, accommodation, fighting positions and bulk petrol storage, emerging at the foot of the North Face of the Rock.