Ardee Castle is the largest fortified medieval Tower House in Ireland or Britain.

In 1641 Sir Phelim O'Neill took possession of the town and set up the Irish Army headquarters, but on the retreat the town and castle were retaken by the English Forces under the command of Sir Henry Tichborne, a garrison was then placed and O'Neill's rear-guard was defeated.

In 1690 the castle was used by James II as his headquarters prior to the Battle of the Boyne.

The rectangular building stands four storeys high, with turrets situated at the north-west and south-west angles, the main entrance was protected by a machicolation on the outside, with a 'murder-hole' on the interior.

The ground floor has a rounded barrel vault, and access to the upper storeys is by means of a stairway in the north-west turret.