The most popular starting point for the ascent of Beinn a' Chaisteil is Auch on the A82, however parking is extremely limited there and guide books recommend starting at a car park at at the head of the glen and using the West Highland Way to walk down to Auch. A direct ascent of Beinn a' Chaisteil is possible from the foot of the Auch Glen but this is a very steep climb on grass with a few crags higher up which can be avoided. A less strenuous alternative is to walk up the Auch Glen for 2.5 km to the ancient burial ground and then climb SE to the col between Beinn a' Chaisteil and Beinn nam Fuaran from where both hills can be climbed. As noted Beinn a' Chaisteil can be ascended as part of the round of the five Auch Corbetts and is the last hill of the day to be climbed.