Roosky sits on the River Shannon where Roscommon and Leitrim meet, a small village split by the river and held together by a bridge. The Shannon here is navigable—boats pass through daily, pleasure craft mostly, and the occasional commercial vessel still working the inland waterway.
Roosky Lock manages the water level, letting boats up and down. It is a working lock, not a tourist attraction, though tourists watch from the bridge. The real business is the water moving north and south, and the boats waiting their turn. The village itself is secondary to the river.
The reason to come back. The things every local will eventually tell you about, usually after the second pint.
About 30 minutes north of Roscommon town on N63. The Shannon is the landmark; once you see the river and the bridge, Roosky is there.
Limited local services. North to Carrick-on-Shannon is the realistic option for public transport.