Are you heading to Belfast? The Antrim Round Tower is open all year round and it's completely free to look at. The tower was built around the 10th century as a bell-tower for protection from raiders. It is 28 metres tall and is one of the finest of its kind in Ireland.
Known locally as 'The Steeple', it is a great reminder of the Antrim's monastic settlement. Although the tower is tall, it is quite difficult to see from the road. It was probably founded by St. Aebh in 495 AD, although both Comgall and Durtacht have also been suggested.
There are lots of exciting attractions available nearby, so have a look at the website linked for more inspiration during your trip.
Concessions: Free entry