There is nothing to see at Derrylea. That is precisely what makes it interesting. Somewhere beneath improved pastureland in County Kildare, up to five small enclosures lie invisible to anyone standing in the field, detectable only from the air, where differences in crop growth betray the outlines of buried features below.

The enclosures were identified as cropmarks on an aerial photograph. Cropmarks form when buried ditches or walls affect the soil's moisture and nutrient content, causing the crops or grass above them to grow at slightly different rates, producing patterns legible only from altitude and usually only in dry conditions. The five features here are closely associated, occupying a roughly rectangular area approximately 270 metres east to west and 150 metres north to south. The location is telling: the land sits near the confluence of the Black River, flowing southward, with a small eastward-flowing tributary that traces what was once the course of the River Barrow itself. This kind of low-lying ground, formerly prone to flooding and sitting at the junction of two watercourses, is precisely the sort of place where early settlement activity concentrated, with water offering both resources and natural boundaries. By 1939, when the Ordnance Survey last recorded field boundaries immediately to the south of this area, some of the enclosures' immediate landscape context was already being simplified. Those boundaries have since been removed entirely, and the fields give no hint of what lies beneath them.