While a good few people visit Charles Fort in Summercove (near Kinsale) many drive from Kinsale and so miss a very pleasant walk. Plus they face the "fun" of driving in Summercove to get to the fort (a village that was most definitely not built with cars in mind!!)
Go to the Spaniard Pub just at the edge of Kinsale (anyone will be able to give you directions). Just across the road is a laneway - go down the hill and turn left and walk to Summercove along the coast with great views of both Kinsale & Summercove (this is pedestrianised - do NOT attempt to take a car along this road!). Be warned though that there's a lot of wild garlic growing in the area so it can be a bit smelly there at times - nice smell if you're fond of your food though and it keeps the vampires away ;-P
Also there is quite a steep hill at the end of the walk, followed by a walk down into Summercove and up another hill to the Fort. Still the whole walk only takes around half an hour one way so it's not exactly strenuous & is far more picturesque than the car trip!!
After visiting the fort, stop for a drink at the Bulman pub in Summercove, where you'll find loads of people sitting outside admiring the view in the Summertime - a very pleasant way to spend a lazy afternoon.
Take a trip by bus to the goumet city Kinsale. The trip takes less than one hour. Kinsale is a beautiful boating place with plenty of restaurants and cafes.
I recommend to take a walk to the ruins of James Fort and its Blockhouse (see photo). From there you have a scenic view to the fishing village Scilly, to Kinsale and to the Charles Fort. For that walk you can pick up a free leaflet at the Tourist Office.