Fort William is the largest town in the Lochaber area so is a great base for exploring the many historical sites around.
Nearby is Inverlochy Castle built in 1280 and a short walk from the town centre at the mouth of the River Lochy. This is a lovely flat gentle walk and worth a visit on a nice day. Just beside it is the new Highland Soap Company's Gift Shop and Cafe - a perfect stop for coffee and cake!
Castle Stalker can be found close the shore at Port Appin between Glencoe and Oban.
Slightly further afield, you can get to Urquhart Castle on the banks of Loch Ness in about an hour in the car and about a 90 minute drive away is the instantly recognisable Eilean Donan Castle, near the bridge over to Skye.
Another site worth a visit is the WW2 Commando Memorial near Spean Bridge which is about a 15 minute drive away.