Picking up on Mardee's comment about Inverness - it is very much a 'marmite' type of place. People either love it ir hate it. I actually like the city. Yes it is tourist central but then so many other places beloved of the tourists are too. Don't bother with all the Nessie hype and Urquhart Castle is always busy. The best way to see the castle is from a cruise on Loch Ness.
Culloden Battlefield is on most tick lists but is probably best appreciated if you have an understanding and interest in Scottish history and the Jacobite Rebellion.
Near Culloden is Clava Cairns which are worth visiting, especially if you are fans of Outlander. They are supposed to be the inspiration for Craig na Dun. The cairns were part of a Bronze Age cemetery dating from 3000-4000 years ago. They are best visited early evening after all the other tourist have gone and the lower light is much more evocative. I've always found them a magical place.
The other place worth considering is Fort George which was built after the Battle of Culloden to subdue the Highlands. It is virtually unchanged since it was built and still remains one of the largest and most impregnable fortifications in Europe. Impressive just doesn't begin to describe it. Allow plenty of time as there is a lot to see. It is still used by the military and soldiers can be seen around the site.
By the time it was finished, the Highlands were relatively calm and no action was ever required from Fort George. There is a story, may be apocryphal, that one shot was fired by a jittery soldier on night duty who thought he saw a Jacobite soldier creeping up to the fort and fired at him. Next morning the guards found the dead body of a cow....
Jutting out on a peninsula into the Moray Firth, this is also a good place to see bottle nosed dolphins.
Another choice could be Dunrobin Castle, the family home of the Dukes of Sutherland and the largest and most northerly of Scotland's Stately homes. Again it is impressive. There are more pictures and information here. Check out train times. Dunrobin Halt is a request stop, so make sure you tell teh ticket Collector(Guard) when you get on the train that you want to get off there. He'll then tell the driver. On the return trip, stand in clear view of the arriving train and hold you hand up high as a signal you want the train to stop.
So don't be discouraged from using Inverness as a base. There's a lot you can do from there.
