On a budget, weigh it — Malahide Castle & Gardens isn't cheap for what it is.
€14–€16 castle; grounds free
A storybook castle with a guided interior, a lovely walled garden and butterfly house, and grounds that make for an easy family half-day reachable by DART. The honest catch: the interior tour is short and the castle is fairly modest inside, so the real draw is the grounds — less compelling on a wet day.