Phoenix Park is the largest enclosed urban park in any European capital, and it wears its size lightly: seven hundred-odd hectares of grassland and old oaks where a working president, a zoo, an ancient deer herd and a steel cross the height of a building all share the same wide sky. Do it in the morning, on legs that don't mind a long flat walk.
Start at the Parkgate Street end, under the Wellington Monument — the tallest obelisk in Europe, its base cast from captured cannon. Walk west past the People's Flower Gardens and the zoo's edge, then out along the main avenue, where the Áras (the President's house) sits white behind its railings. Push on to the open grass of the Fifteen Acres for the Papal Cross, stark on the green, and the fallow deer that have grazed here since the 1660s — keep your distance and let them ignore you.
The turn comes at the Magazine Fort, the star-shaped powder store on the bluff above the Liffey. Climb up for the river view, then drop to the Castleknock or Chapelizod gate and the bus back into town.