Which Dublin sights should you book ahead?

What most people said

• Most say book Kilmainham Gaol well ahead; leftover same-day tickets are released online each morning but go in minutes.
• Book of Kells/Trinity College should be booked ahead; many recommend the student-led campus tour bundled with the Book and Long Room.
• Guinness Storehouse is self-guided; opinions split, with several preferring the Jameson distillery or a pint in a proper pub.
• Walk-up options: free National Museum, Natural History Museum and National Gallery; 14 Henrietta Street is a well-liked Kilmainham alternative.

What people said

• Kilmainham Gaol is a good one to order ahead of time. If you do not, go on the official website right at 9:15 the morning you want to go. That is when any remaining same-day tickets are released.
• We couldn't get tickets for Kilmainham Gaol and we also went to 14 Henrietta Street. It was so interesting - we really enjoyed the tour and learning the history!
• We did and it was fine. In hindsight I would skip it and fill that time in a pub drinking a proper pint. You don't see the brewhouse and it felt super corporate marketing campaign.