The National Museum is actually 4 seperate museums, 3 of which are in Dublin – Archaeology, Decorative Arts & History, and Natural History. So this is actually 3 things to do for free in Dublin. Archaeology houses over 2 million artefacts including amazing treasures from Prehistoric and Viking & Medieval Ireland. The Iron Age bog-bodies are fascinating. Decorative Arts & History exhibits a broad range of objects including furniture, weaponry, ceramics & items of folk-life & costume while the Natural History museum is a fascinating, unique display of animals from Ireland & worldwide, an incredible place containing 2 million+ specimens including a massive Blue Whale skeleton and extinct species. Each are open from 10am – 5pm Tues. - Sat., 2pm – 5pm Sun. & closed Mondays. Entrance to each is free.