Inis Oirthir (Inishsirrer) is an uninhabited island found 600 metres off the Glashagh Lower coast in Gweedore. The island is 2 kilometres long and is about 300 metres wide at its widest point. Inishsirrer has the ruined remains of 10 or so buildings and is grazed by a flock of sheep. At the south-east end of the island, nearest mainland Donegal, is a large freshwater lake which attracts a huge amount of migrating birds and it is not unusual to be in the company of hundreds of Barnacle Geese as you arrive on the island.
All the climbing on the island is concentrated on the excellent very sheltered crags at the north end of the island. To find the crags from any place on the island, simply walk towards the small lighthouse.
Access to Inishsirrer is under your own steam by sea kayak from the public piers at either Port Arthur or Buninver. The sea passage is short and well sheltered by a chain of skerries running landward from Inishsirrer. The only pier on the island only really works at high tide as it is high and dry the rest of the tide states. If the sea is good there is an excellent little sandy beach just to the south-west of the crags at the northern end of the island.
There is no fresh water on the island as the lake is slightly brine and usually heavily birded.
The climbing on the island is on the crags below the small lighthouse at the north end of the island. Access to the base of the crags is by abseil or very careful downclimbing.
The rock on Inishsirrer is very different from the neighbouring islands of Umfin, Gola and Tororragaun as it is covered in a thin black lichen. This lichen is incredible to climb on when dry but alas has no friction at all when damp or wet.