St. Nicholas Gate, also recorded as Asculf's Gate and St. Patrick's Gate, has left no trace above ground; the 1863 Ordnance Survey map marks it only as a site, and today there is nothing to interrupt the ordinary rhythm of the street. That absence is itself a kind of puzzle, given how substantial the structure once was. A survey from 1585 describes a gate flanked by two round towers on the outer face and two square ones within, each tower rising three storeys to a height of around 14 metres, with four arrow loops per storey and walls 1.5 metres thick. A portcullis controlled the passage. It was, by any measure, a serious piece of defensive architecture.

The gate appears in the written record as far back as 1250, when the Dublin White Book recorded a lease of the tower beside St. Patrick's Gate to one Richard Chartris and his wife Agnes, at four shillings a year, on condition that they maintain the buildings at their own expense and allow free passage through. Around 1252 a further grant gave Reimund of Poitou custody of the entire gate for life, cellars and all, for half a mark annually. By 1466 the Dublin Assembly Roll shows a citizen named John Boulond receiving a life grant of the gate, then called Seint Nicholas Yate, for the modest rent of eightpence a year. In 1535 a merchant, William Queytrott, was granted the old tower over the gate in perpetuity, for his male heirs, on the condition that he build two flat lead-covered storeys on top within two years, at his own cost, and keep the structure in repair; the city, for its part, retained the right of entry whenever the gate needed defending. The gate is also probably identifiable with Hascuff's Gate, mentioned in a document from 1534, a name echoing the Hiberno-Norse past of the city. It appears clearly labelled on John Speed's map of Dublin, published in 1610.

The site is on Nicholas Street, close to the area around St. Patrick's Cathedral, and is accessible simply by walking the street. There is nothing to see at ground level; what the spot rewards is the imaginative exercise of reading the 1585 survey description against the present streetscape, calculating 14-metre towers and a portcullis into a space that now offers no physical clue to any of it. The 1863 Ordnance Survey map, viewable through the Ordnance Survey Ireland website, is useful for fixing the precise location. Speed's 1610 map of Dublin, which labels the gate as entry number 45, gives a sense of how it sat within the broader circuit of the city walls.