I am wanting to go to Culloden Battlefield, Cowdor Castle & Clava Cairins. I know they are close to each other. Any suggestions on how to get there using local transportation.
Having no need to travel to any of these places using public transport because I have my own car, I'm not able to advise you.
However I would suggest you contact Culloden Battlefield and Cawdor Castle direct and ask your questions. Then you will receive up to date information from the people on the ground about the best way to reach them. You surely will not be the first person to want to visit using public transport. Not everyone has a car, or chooses to travel by car. That said I'm not sure you can reach Cawdor Castle by bus and a taxi might well be the only way to do this. Do you want to visit both these places on one day?
The Clava Cairns are close to Culloden and it might be possible to do this journey on foot if you choose to. I've been to the cairns from Culloden by car and have to say I did not notice a designated public footpath from one to the other, so you would be walking on the road. As far as I know there is no footpath (sidewalk) so you might not want to walk anyway, although the road would not likely be too busy with vehicles. If you did want to walk it would take about 30 minutes which could be quite miserable if the weather is wet, because it does sometimes rain in Scotland :-).
It may be that the easiest option for you would be a taxi from Culloden to the Clava Cairns and back again. No doubt the good folk at Culloden would be able to advise you about that.
If you have accommodation in Inverness already booked, then contacting your hosts to ask about the best way to travel to the places you want to see might also be a good idea. Nothing beats local knowledge.
Hope this helps.
If you Google Cawdor Castle and Clava Cairns and click on the links for how to get to them, you'll see some of the options. The link is obviously under "Finding Us" on the Cawdor website and not so obviously under "more pages" on the Clava one.
We took a local public bus from Inverness to the Culloden Battlefield. We didn't walk the 300 yards to the Cairns. I loved the bus. We rode with local residents going about their daily business.
Taxi or train + taxi seem to be the only options for the castle if you don't have a car.
Another method I use, especially if the information on a venue's web site is lacking, is to "google map" the venue and then select "directions." Doing so, I see that Culloden Battlefield is a 40 minute bus ride from downtown Inverness and Cowdor Castle is a 35 minute bus ride from Nairn. Google even provides you with the bus numbers...
BTW: Google maps and other transportation travel planning web sites (like Transport for London) are the number one reason I ALWAYS get a local SIM card for my phone.
Even if you are not staying at one of the bigger hotels; some can book small tour groups (Vans) that you can join for a reasonable fee if your time is valuable to you.
Inverness has one of the BEST Tourist Information Offices I've ever used. They helped us with local bus routes and numbers, and booked tours for us, too. The staff are friendly and professional and extremely helpful!
The public bus is very easy to use to get out to Culloden Battlefield. I walked over to Clava Cairns from the Battlefield. As Toni mentioned the TI is very helpful. Also, I suspect that a taxi to Cawdor Castle might be amazingly affordable. It's just past the airport.
As long as you don't mind walking, as others have said, you could walk from Culloden to Clava Cairns -- I'd guess a 20-30 minute walk. They are really just out in the farms, I don't believe any public buses go there (Clava Cairns) directly. There are some tight little farm lanes, so you do need to watch out for traffic.