On a steep slope about 13km (8 miles) north of downtown, this 12-hectare (30-acre) garden was first planted in 1875 and is best known for its 2,000 varieties of rhododendrons. Peak bloom time is in May and June. Also on the grounds is the National Transport Museum of Ireland (tel. 01/832-0427; www.nationaltransportmuseum.org), a collection of public-service vehicles from the 1880s to the 1980s. It's probably one for enthusiasts, but charming in its own way. Note: The footpaths are not properly kept up and can occasionally be treacherous, so you should come prepared for hillwalking, rather than if you were visiting a public park.