Morning: coffee at Lanesbrew or Cata Coffee, then down to the quay for a boat trip out onto the lake. Ask about stopping at one of the islands.
Afternoon: drive 15 minutes east to the Corlea Trackway, then loop back past Rathcline Castle.
Evening: book a session at The Sweaty Yeti sauna, then a tasting at Lough Ree Distillery (book ahead), dinner in town and a walk across the bridge as the sun goes down.