An Caisteal is usually ascended from Glen Falloch — there is a large lay by for parking on the A82 at grid reference although it is also possible to start from Derrydaroch farm 2.5 kilometres to the south west. The route goes under the railway by a sheep creep and follows a track by the River Falloch upstream for about a kilometre before striking SW to climb Sròn Gharbh direct across pathless grass. A path is then picked up at the summit of Sròn Gharbh which leads across Twistin Hill and past The Castle rocks to reach the summit.