There is an easily accessible example of a souterrain, or earth house, located at the foot of Knock Ullinish. It is a short walk from the minor road to Ullinish, close to Dun Beag at Struan. To reach it, leave the road via the gate at NG332382. The first few steps are boggy when wet, but you soon pick up a natural track that leads round towards the north of the small hill of Knock Ullinish. You will find the entrance to the souterrain at NG333384. It may not be immediately obvious, but the picture below should help you to identify it.
It is a very narrow squeze to get inside, but it's not for the claustrophobic - or the overweight!
The passageway is about 6m long to the point where there has been a collapse of the roof. The first section, seen here, is just over 1m in height and just under 1m wide. It gets considerably wider further along the passageway. As ever, a torch and waterproof trousers are recommended accessories.