We drove into Limerick City to where the magnificent Shannon River meets the salt water of the sea. In this most strategic location we found St. John's Castle sitting along the river on it's own King's Island. This is the place where fleets of Viking vessels entered the river to raid and put fear in the hearts of the Gaelic Irish. People of different cultures and varied intentions sailed into Ireland through this port. King John's castle was built in 1200 not long after the Norman Invasion. It was a watchdog on the sailors and their many cargoes, human and otherwise. There was fear in the hearts of many captains as he guided his vessel past the scrutiny of the eyes of the mighty St. John's Castle at Limerick.

The castle has five drum towers and tall curtain walls. There has been excavation carried out here that has uncovered many important artifacts and a small Viking village. Also found was a soldier's diary that logged the horrors of a siege on the city.

The castle is open to the public and one can see the extent and character of the excavations that are happening there. There are also exhibits of over 800 years of Limerick's turbulent history.