Charleville Castle stands on the southern edge of Tullamore, surrounded by some of the oldest oak woodland in Ireland. It was built between 1798 and 1812 to the designs of Francis Johnston — who also designed the GPO in Dublin — in a dramatic Gothick Revival style with towers, battlements, and pointed arches. The interiors retain original decorative plasterwork and a grand staircase, though much of the building is in a state of romantic dilapidation.
Tours of the castle run regularly and take visitors through the main rooms, the dungeons, and the grounds. The woodland walk is worth doing regardless of a castle tour — the ancient oaks create a canopy unusual in the relatively treeless Irish Midlands. The whole site has an atmosphere that is hard to manufacture: genuinely old, genuinely atmospheric, and without the heavy-handed heritage industry polish of more famous Irish castles.