From October to April the castle opens Wednesday to Sunday and bank holiday Mondays, 10.30am to 5pm, last admission 4.15pm; from May to September daily 9.30am to 5.30pm, last admission 4.45pm; closed 23 to 27 December inclusive. Guided tours are available and group tours must be booked by phone or email. Free admission for everyone on the first Wednesday of each month, first come first served. The council park around the castle opens daily from 10am, closing at 7pm in October, 5pm in November to January and later through the summer.
OPW notes that the castle currently has no phone or internet connection, so the published number may not answer. Wheelchair ramps give full access to the tea room and the castle, with a lift inside, accessible toilets and designated parking; baby changing, bicycle parking and a cafe on site; no shop listed.
Dogs: Pet dogs on a lead may use the free council park around the castle but are not admitted inside the castle, where only assistance dogs are allowed. Dogs on a leash may walk the paths, woodland and pond areas of Rathfarnham Castle Park during park hours; whether they may enter the playgrounds is not confirmed.
Photo: Rathfarnham Castle's whitewashed Elizabethan house with its square corner towers and a rounded Georgian bay, and the low courtyard range to the left, under a broken blue sky. PaulT, CC BY-SA 4.0. Source: https://commons.wikimedia.org/wiki/File:IRL_Dublin_Rathfarnham_Castle_01.jpg. Licence: https://creativecommons.org/licenses/by-sa/4.0. Resized and cropped for display; derivatives retain the source licence.