Rath Croghan today, is a complex of earthworks and other monuments approximately 5km northwest of the village of Tulsk, in County Roscommon.
There is no townland enshrining the name Cruachain, the name has survived in folk memory as Rath Croghan (Rath Cruachain), the name of the largest and most important Mound in the complex.
Archaeologists are reasonably sure that the site has been properly located, we do not know if the name referred originally to the region or to a specific group of monuments.
Some 49 monuments have been numbered in the Cruachain complex.
Generally, in elevated situations in the rolling limestone countryside.
Unlike at Tara, there is no great enclosure forming an obvious centre, but the large mound at Rath Croghan seems to be the focus around, which the other earthworks were grouped.
Around this are clustered the various enclosures and tumuli.
There is a noticeable quantity of ring barrows.
One of the larger earthworks is known as Dáithí's mound and it is crowned by an unhewn monolith standing on a height of 1.8m.
Other ancient features in the area, are 5 linear earthworks, arranged in parallel pairs, some to form avenues of a type reminiscent of the 'Banqueting Hall' at Tara.
All apparently oriented towards the main concentrations of tumuli, the largest, at Glenballythomas, runs 640m from east to west leading directly to Rath Croghan and its outliers. Best preserved, but considerably shorter, are the northern 'Mucklaghs' the banks of which still stand to a height of 2.4m.
Ancient field boundaries detectable under the modern field patterns are not necessarily prehistoric, and there are also, several miscellaneous enclosures and a large number of ringforts, which are likely to be of post-Iron Age date.