Ballinastoe is Ireland's first red-standard (difficult/severe) dedicated mountain bike trail centre. Well worth a day trip.
Cloon Wood has long been a popular DH track in close proximity to Dublin, regularly hosting rounds of the NPS DH Series.
An excellent MTB location close to Dublin that has hosted many NPS XC races. Contains an extensive network of single track trails built originally over some years by a local MTB legend, with some further input from the good people at EPICMTB. Technical in places with some DH style descents. Possible to link to Ballinastoe via the Wicklow Way to extend the riding further.
A variety of riding in and around the world famous Monastic site. Some big climbs rewarded by fantastic single-track descents and amazing views.
Plenty of brilliant trails to choose from here which will throw everything at you from switchback climbs to roots, twists, turns, rocks and more roots. Relatively short trails but technical and flowing in places and well worth a visit if in the area.
Overall you have two forests to explore, the second forest has a downhill course and some great XC forest singletrack. Lots of great trail building and maintenance work by Epic MTB and other local clubs. Get out and explore it!!
Slade Valley has hosted various XC events in the past including Leinster League and NPS races. For the past number of years the IMBRC (Irish Mountain Bike Racing Club), with much help of a local EPIC MTB member, have been building and maintaining the many km's of trails there.
This popular way-marked route may be the traditional stomping ground of the red-sock brigade, but is a SUPERB setting for great mountain-biking.
A popular biking spot for years due to its close proximity to Dublin City and now with sanctioned XC trails. Lots of variety in other unsanctioned trails around the hill.