Yesterday I visited Aughanure Castle ("OCK-a-nure"), a restored tower house (built c. 1500) in a tranquil riverside setting not far from Galway City, and as you can see I couldn't have asked for better weather. (Bats, murder holes, secret chambers...I imagine it might be rather spooky to visit when the weather's not so fine.)
That pepperpot-tower-type thing used to be a watch tower, but most of the wall that connected it to the others is gone (or under grass). Too bad they don't allow picnics here!
The forty-minute walk from Oughterard is do-able but not ideal, since there are a few spots along the busy N59 without a shoulder to walk on—and Oughterard isn't the most happening spot anyway. Seems there are as many closed (some quasi-derelict) shops and restaurants as there are ones still open for business. If you don't have a car, going by Citylink (as I did) may be your best option. Ask to be dropped off at the castle turn-off, which is about 1.5km before you reach Oughterard. It's a very pleasant 2km (20-minute) walk from there.