The medieval quarter occupies the northern end of King's Island, the small island between two arms of the Shannon that has been the heart of Limerick since the Vikings arrived in the 9th century. The street plan is recognisably medieval: narrow lanes, a single main street (Nicholas Street) running between the castle and the cathedral, and the ruins or restorations of the original town walls along the river.
The walk is short — from King John's Castle to St Mary's Cathedral is five minutes, and the loop through the surviving Bishop's Palace, the Limerick City Museum, and the Treaty Stone monument on the opposite bank can be done in an hour. A guided walking tour leaves several times a day from the castle in summer; for the rest of the year the self-guided trail signposted along the streets is enough.