On relatively low-lying land to the north-north-west of Baldongan Church in County Dublin, an ancient field system, possibly incorporating a roadway, falls firmly into the second category. There is nothing to see from the surface. The evidence lies entirely in crop marks, those subtle discolourations in growing vegetation that reveal buried features below, captured in a Digital Globe orthoimage taken sometime between 2011 and 2013.

Crop marks form when buried walls, ditches, or trackways affect how overlying soil retains moisture, causing the crops or grasses above to grow at slightly different rates or to ripen at different times. Viewed from above at the right moment, these variations show up as faint lines and shapes that correspond to structures long since ploughed out or silted over. The Baldongan field system was identified through such imagery and recorded in the Sites and Monuments Record, with additional detail provided by T. Condit. Beyond that, the record is spare: a field system of uncertain date, possibly ancient, possibly containing a roadway of some kind, sitting in the agricultural lowland near a medieval church that itself carries a complicated history. The compiled record was put together by David O'Connor and updated by Christine Baker, with the entry uploaded to the national record in November 2014.

Baldongan Church, which sits to the south-south-east of the field system, is a more visible landmark and serves as a useful point of reference when trying to orientate yourself in the area. The field system itself offers no surface remains whatsoever, so a visit in the conventional sense yields little beyond a sense of the landscape and its texture. The crop marks that revealed the site would only be visible from the air, and then only under the right agricultural and seasonal conditions. For those with an interest in remote sensing or the methodology of landscape archaeology, the site is a useful illustration of how much can remain encoded in ordinary-looking farmland, waiting for the right angle of light or the right stage of a crop cycle to briefly surface.