There is nothing to see at Derrylea. That is, in a sense, the point. Somewhere beneath an ordinary stretch of improved pasture in Co. Kildare, up to five small enclosures lie completely invisible to anyone walking the ground, detectable only from the air, where they show up as cropmarks, the faint differential browning or greening of crops and grass caused by buried features affecting soil moisture and depth. It is archaeology legible only to cameras and pilots, and even then only under the right conditions.

The enclosures were identified from a single aerial photograph, and together they occupy a roughly rectangular area approximately 270 metres east to west and 150 metres north to south. What makes their location interesting is the hydrology. They sit on land that was formerly liable to flooding, close to the confluence of the Black River, which flows southward along the eastern edge of the group, and a small eastward-flowing tributary to the south, a watercourse that follows what was once the old course of the River Barrow itself. Settlements and enclosures near river confluences are a recurring pattern in the Irish landscape; such spots offered water, transport, and defensible ground, though the specific date or function of these particular features is not known. Field boundaries visible on the Ordnance Survey six-inch map of 1939 once ran immediately south of the site, but those too have since been removed, leaving the ground still further smoothed of its older layers.