In the southern sector of Europe's largest enclosed urban park, aerial imagery reveals the ghostly outlines of practice trenches, their crenellated lines pressed into the soil and readable only from above, rendered visible as cropmarks when moisture or soil disturbance causes overlying vegetation to grow differently along buried features.

The trenches were identified through Google Earth imagery captured on 28 January 2017, compiled by Caimin O'Brien from details provided by John Mulligan and uploaded to the record in May 2020. Two sets of the characteristic zigzag lines are visible: one cluster in the southern portion of the park, and a second, similar set of crenellated markings approximately 60 metres to the north-north-west. The crenellated or stepped layout is typical of First World War trench design, where straight lines were deliberately avoided to limit the blast radius of shellfire and prevent an enemy from firing along the full length of a trench if they broke through. Practice trenches of this kind were dug at numerous sites across Ireland and Britain during the war, allowing troops to train in the techniques of trench warfare before deployment to the Western Front. The Phoenix Park, with its open ground and proximity to military infrastructure in Dublin, was a logical location for such an installation.

The trenches are not marked or signposted on the ground, and there is nothing obvious to see during a regular walk through the park. The cropmarks are most meaningfully viewed through aerial imagery, where the crenellated patterns stand out against the surrounding grass. If you do visit the southern sector of the park, the area around Chapelizod, the ground itself will appear unremarkable, a broad open expanse of turf with no visible earthworks. The value here is in the looking rather than the standing, in pulling up a satellite image and letting the geometry of a wartime exercise ground emerge quietly from the green.