The Grand Canal Way is a 117 km trail that starts in Lucan in West Dublin and follows the towpath of the canal to Shannon Harbour on the River Shannon in County Offaly owing to the fact that the trail follows a canal, it has a very flat profile with just 196 meters of elevation gain across the trail.
The trail isn't ideal for camping but for a walking holiday break staying in B&B's it's ideal. You could gladly wander from town to town sampling the culinary expertise while continuing on the next day on a relatively simple walk.
This won't be one of the most inspiring trails you have done, but what it lacks in spectacular nature, it gains in its simplicity. If you haven't walked a long-distance trail before, you can't go wrong with this. It can make a great trail to get a good pace upon as well. Many will easily clock 6-6.5km per hour on the trail without much bother.
Photo 1 credit to William Murphy under CC BY-SA 2.0