The "Crag" and "Cave" system at the Herts Young Mariners Base was built in 1998 and offers opportunities for all to practice their techniques in a friendly environment before traveling to the natural outcrops and caves of Derbyshire or Wales.

The Crag incorporates leading features in climbing wall technology including "live" leading systems as well as easy slabs for the novice or the timid. For the experts overhangs, chimneys and cracks should provide sufficient challenge to keep them absorbed for hours.

The Cave, complete with tubes and squeezes brings the world of caving to life in a system that extends for over 100m. Particular features include cave paintings, fossils and a stream passage. The introduction of both horizontal and vertical techniques can all be covered within this system, the use of wire ladders and S.R.T. (single rope technique) can be taught in a safe environment.

The system has been featured in tv programmes such as "Out and About", "Grange Hill", and "Holby City"