Rathcroghan is a complex of archaeological sites near Tulsk in County Roscommon, Ireland. It is identified as the site of the traditional capital of the prehistoric and early historic rulers of the western territory. The Rathcroghan Complex is a unique archaeological landscape with many references found in early Irish medieval manuscripts.

This landscape consists of 240 plus archaeological sites, sixty of which are protected national monuments. These monuments range from the Neolithic (4000 – 2500 BC), through the Bronze (2500 – 500 BC) and Iron Age (500 BC – 400 AD), to the early medieval period and beyond. These monuments include burial mounds, ringforts and medieval field boundaries amongst others.

Rathcroghan is said to provide entrance to the Otherworld, described in the medieval period as "Ireland's Gate to Hell",

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