Suilven forms a steep-sided ridge some 2 km in length. The highest point, known as Caisteal Liath (the Grey Castle in Scottish Gaelic), lies at the northwest end of this ridge. There are two other summits: Meall Meadhonach (Middle Round Hill) at the central point of the ridge is 723 m high, whilst Meall Beag (Little Round Hill) lies at the southeastern end.
Geologically, Suilven is formed of Torridonian sandstone, sitting on a landscape of Lewisian Gneiss. As the softer surrounding rocks eroded, a process whose duration can be counted in hundreds of millions of years, Suilven was left as an Inselberg, an "island-mountain", hence its prominence.
From the coast to the west Suilven looks like a large grey pillar, hence the name which it was given by sea-borne Vikings. From the inland side the mountain has more of the appearance of a pyramid.