Papa Stour sea caves were described as some of the finest in the British Isles by the naturalist J.R. Tudor in his book, "The Orkneys and Shetland," written in 1883. The Holl o Boardie, which passes right through the north-west tip of the island, is nearly half a mile long and wide enough to take a RIB through. Fogla and Lyra Skerries are also pierced through by several large caves.