Dublin Castle is more of a palace than a castle and is currently used to entertain heads of state. It was originally built on the orders of King John in 1204 and has enjoyed a somewhat quiet history. Silken Thomas Fitzgerald laid siege in 1534, a fire destroyed much of the castle in 1684, and the events of the 1916 Easter Rising. It was lightly defended in 1916 and probably would have fallen if the insurrectionists only realized how light the opposition was they faced.
The castle was used as the official residence of the British viceroys of Ireland, until the Viceregal Lodge was s built in Phoenix Park. Earlier it had been used as a prison. Red Hugh O’Donnell, one of the last of the great Gaelic leaders, escaped from the Record Tower in 1591, was recaptured, and escaped again in 1592. Only the Record Tower, built between 1202 and 1258, survives from the original Norman castle. Parts of the castle’s foundations remain, and a visit to the excavation is the most interesting part of the castle tour. The castle moats, now completely covered by modern developments, were once filled by the River Poddle and can be seen on the castle tour.
Dublin Castle is easily reached from The Anchor Guesthouse on foot. See the attached map below. Perhaps Trinity College, The House of Lords, & The Guinness Storehouse might be toured on the same walk.