The oval measures roughly fifty metres east to west and thirty metres across, and to a casual eye it reads as nothing more than a slight unevenness in the landscape, the kind of thing you might walk over without a second thought. That unremarkable surface covers a site with a documented history stretching back to at least the thirteenth century, and quite possibly much further.

The church here was dedicated to St. Machtus and was known locally as the 'white chapel'. It disappears from the record around 1490, according to Ronan, writing in 1940. Before that, it appears in two separate medieval taxation records, from 1292 and 1294, and is listed as the church of 'Culmyn' in the Crede Mihi, a registry of the churches of the Dublin diocese compiled around 1275. That document is one of the key sources for understanding the ecclesiastical geography of medieval Leinster, and the appearance of Coolmine in it suggests the site had genuine parochial standing rather than being a minor dependent chapel. The former grounds of Coolmine House once enclosed the oval area, keeping it within a private demesne for centuries, before the land eventually became part of the Blanchardstown Millennium Park.

In 2009, ahead of the proposed Metro West transport project, the site was subject to a geophysical survey (licence no. 09R195). That survey identified remains of enclosure ditches and possible pit features associated with both the church and its graveyard, as well as a sub-circular enclosure of around fifty metres in diameter and further ditch remains extending south and east. Some of the features showed possible burning, which Nicholls suggested in 2009 might indicate hearths or kilns. The site is now within the Millennium Park and can be visited on foot, though there is little to interpret on the ground without some prior knowledge of what to look for. One detail worth noting: a dog run was installed directly against the eastern edge of the oval area, apparently without archaeological supervision, which gives a sense of the pressures these low-profile urban sites continue to face.