Most of Ireland's tunnels date from the 19th century in the building of the railways, typically excavated through rock by blasting and then hand excavation.
Historically, a number of country estates had tunnels, both to provide privacy (and means of escape) and to keep the views from the house clear of servants and labourers.
Stone and brick built sewers are often mistaken for "tunnels", in particular in central Dublin.
For example, at Dunkettle in Cork, to construct the interchange at the north end of the Jack Lynch Tunnel, a section of railway approximately 100 m long was covered so that the N25 (now part of the M8) could cross the railway at a shallow angle - a "cover only" tunnel.
Several large diameter drainage tunnels exist: Dublin: Kilkenny: