Ennistymon’s name could be linked to its physical features. The steep hill on which it stands is partly natural and partly artificial. Some historians claim that Ennistymon’s name INIS DI MAIN refers to the island of the middle house. In 1564 the O’Briens of Thomond acquired a castle in a wooded estate by the cascading Cullenagh river. This castle was known as the "middle house", being central to the O’Brien castles at Dough and Glann. Today the Falls Hotel (formerly Ennistymon House) occupies the original castle site. Ennistymon is hidden in a recess among the hills. It lies on the southern edge of the Burren, two miles inland from the Atlantic. The narrow street near the bridge over the Cullenagh River is the oldest part of the town. A little below the bridge, the river rushes over an extensive ridge of rocks and forms a beautiful cascade about 1½ miles away from where it joins the river Derry. The united streams continue towards the sea as the Inagh River. The town developed around this old bridge, the lowest crossing point from the sea the bridge has existed at this point in some form from earliest times .The present bridge (which was originally a toll bridge) was built by the local landlord McNamara in the mid 1790 s.