Off the mouth of Galway Bay lie the Aran Islands, a windblown source of Irish lyric and lore for centuries. The largest, Inis Mór, holds the ruins of several prehistoric stone fortresses, the most famous being Dún Aonghasa, atop a 300-foot cliff over the sea. The so-called Worm Hole is a remarkable rectangular fracture in the basaltic rock of the shoreline. The Seven Churches is a ruin of a medieval Christian enclave, with picturesque ruins and evocative early gravestones. Blue Flag Kilmurvey Beach is a good spot for birdwatching, with a sea colony nearby.