Lough Gur (Irish: Loch Goir) is a lake in County Limerick, Ireland, located between the towns of Herbertstown and Bruff. The lake has a horseshoe shape at the base of Knockadoon Hill and is surrounded by rugged, elevated countryside. It is one of Ireland’s most important archaeological sites. People have lived near Lough Gur since about 3000 BC, and there are many ancient stone structures there.

Near the lake is the Grange stone circle, which is the largest stone circle in Ireland, and a dolmen. The remains of at least three crannogs (ancient wooden islands) are found nearby, and Stone Age houses have been discovered on Knockadoon Hill. Early Medieval house outlines, called "The Spectacles," are also present. Several ring forts are in the area, with one hill fort overlooking the lake. Some of these sites are protected as Irish national monuments.

A legend says that Gearóid Iarla, a 14th-century lord of Munster and poet who worshipped the Goddess Áine, is believed to sleep in a cave near the lake. He is said to ride a silver-shod white horse around the lake when Ireland needs him.

A visitor center, car park, and picnic area are located near Lough Gur. The shoreline is gentle, with a shallow part of the lake reaching the maintained lawn. This makes the area popular for water sports, though motorized boats are not allowed on the lake.

Near the car park entrance is a castle or tower house called Bourchier’s Castle, named after Sir George Bourchier, the son of the second Earl of Bath. It is located at the narrow part of the peninsula where the lake flows around. Along the road to the lake, there are ruins of an early Christian church. At the far end of the lake, the ruins of a Norman castle called Black Castle can be reached by a hillside walk along the lake’s eastern side. This castle was used during the Desmond Rebellions and is likely where the Earl of Desmond claimed authority in 1573 after changing into Irish clothing upon returning to Munster from London.

Lough Gur is famous for finding skeletons of Irish Elk. The National Museum of Ireland – Natural History and Leeds Museums and Galleries in the UK have specimens from Lough Gur.