This is a mortsafe tower, or cemetery watchtower, one of a number erected in Irish graveyards during the nineteenth century in direct response to the trade in freshly exhumed corpses. Body-snatching was a grimly practical problem of the era: medical schools across Britain and Ireland depended on cadavers for anatomical instruction, and legal supply never met demand. The result was a thriving black market, serviced by so-called resurrection men who worked quickly and quietly through the night. Communities responded by posting armed guards over new graves, and in some places, by building permanent structures from which a watchman could keep vigil. The tower at Cruagh is one of the surviving examples.

The structure itself is cylindrical, roughly 3.2 metres in external diameter, and rises two storeys in height, built from roughly coursed granite masonry that sits comfortably against the rocky Dublin Mountains landscape. A parapet level is marked by a slight offset in the stonework. The doorway, which faces north and is of the lintelled type, is now blocked. Light would once have entered the interior through narrow, square-headed window openings. The graveyard it overlooks also contains the remains of Cruagh church and a roughly square granite font. A Rathdown type graveslab, a class of early medieval carved stone associated with the Rathdown area of south County Dublin and typically decorated with motifs such as concentric circles, was recorded here in the nineteenth century by O'Reilly in 1901 and by Crawford in 1913, but it has since disappeared from the site.

The graveyard sits on a steep, grass-covered knoll off Pine Forest Road in the Dublin Mountains, south of Rathfarnham. The approach involves a walk on uneven ground, so appropriate footwear is worth considering. The tower's blocked doorway and exterior masonry are clearly visible from the graveyard, though access to any interior is not possible. The site rewards a slow circuit; the font and the church remains are close by, and together they give a sense of a place that has been in continuous use, and continuous need of protection, across many centuries.