Orkney Islands

You definitely want a car on the main island, called Mainland. There is a local bus service, but the sites of interest are scattered around the island. In 2012, we took the Pentland Ferry into St. Margaret's Hope from Gills Bay, which is only about an hour or so, and the cost was pretty affordable, iirc. Even though our B&B was very close to Stromness and taking the other ferry would have been closer, the Pentland one was cheaper and I liked having the 45-minute drive across the island to orient myself.

The drive from the ferry to Inverness should be around 2.5 to 3 hours, but I would recommend stopping at Dunrobin Castle a bit north of Inverness for a really nice manor home tour with compact but well laid out gardens and a falconry exhibition. We drove from Inverness to Orkney and just took our time, making sure to be at the castle for the morning falconry demonstration after touring the building and grounds, then got lunch before hitting the road. The ferry was supposed to be at 5, but was running about 30 minutes late, so when we got there early at 4, we ended being really early!

There are several things to see on the drive between Orkney and Inverness-- see the map here: http://www.undiscoveredscotland.co.uk/usmapindexes/farnorthern.html

For B&B recommendations, our places in Orkney and near Inverness were both terrific! We stayed at the Pottery House on Dores Beach just south of Inverness, which was my favorite one on the entire trip in England and Scotland. On Orkney, we stayed at the Mill of Eyrland, just east of Stromness.

We've always rented a car locally. I would recommend the same. I would suggest that you consider taking the train to Inverness, renting a car their for a few days, and then taking the train to Thurso and catching the ferry there to Stromness. Rent a car on the island. Contact the local car rentals. I expect that they will likely meet the ferry with a car. Alternatively, you could fly to Kirkwall from Inverness. I know it feels like you should keep the car for the whole trip, but it often does not make sense to do that when islands are involved. :)

My experience...

I took the train from Edinburgh to Thurso and shared a cab to Scrabster. I spent the night at a small hotel there and walked to the pedestrian entrance to the Northlink ferry to Stromness the next morning. It sounds like you could take your rental car on that ferry, but I'd want to verify that before I tried it. If you want to leave your car there in Scrabster or Thurso, you need to check on parking options. Obviously walk-on fares are much cheaper than taking a vehicle.

The ferry terminal at Stromness has direct bus service to Kirkwall. The bus arrived reasonably soon after the ferry did. I enjoyed the cheap bus ride into Kirkwall.

I spent 4 nights at the Shore hotel. It was not cheap, but it was very nice and very convenient for walking around town. In addition to the many sights outside of town, there are some things in town well worth seeing. I especially liked St. Magnus Cathedral and the little Orkney Museum.

By now you've no doubt guessed that I did not have a car. I wanted to spend 2 days doing different small tours, but made my arrangements too late for that. There are tons of tour guides and different kinds of tours. I lucked out and found a one day tour that had room for me. In fact even though I was the only customer, I was only charged the price for an individual. I enjoy these kinds of small group tours because I learn so much from the guides.

Albert is the main shopping street in Kirkwall. I found 2 very useful spots on Albert: Cafelolz@21 and a brand spanking new laundry. I ate at the cafe twice and used the laundry once while I was there. It was at the cafe that I first had beremeal bannocks. I highly recommend it. I had it again at the cafe at Skara Brae, along with a delicious bowl of Cullen skink.

I flew from Kirkwall to Aberdeen on Flybe since I didn't want to backtrack. Flybe also flies to Inverness.

I don't know how many of you "we" are, but how you do this will depend on what's most important to you. If you add up all the options and compare them, the cost difference may be negligible.

If you decide not to have a car on Orkney and/or not backtrack, you might consider driving to Inverness, parking (or as Pamela suggested, returning)
the car there, taking the scenic train to Thurso, taking the ferry to Stromness, taking the bus to Kirkwall, going on at least one small local day tour and flying back to Inverness.

Not knowing what you mean by spring, be aware that the weather is challenging. I was there in mid-May. It was consistently cold and windy. Naturally the day I did my tour, it was also sideways rain about half of the day. And of course it was sunny the next day. Most of the ancient sights are outdoors and require several minutes of walking from parking even if they are not outdoors. The walking tends to be rough and muddy.

why not fly you can get flight from Edinburgh , glasgow and inverness, the glasgow and edinburgh flights do a short stop in Inverness, then hire a car once in Kirkwall.
a car really is very useful on the Island but you can arrange local tours , use local buses and taxis.

Thank you all for the great advice!! I love trains and the idea of renting a car locally is appealing. There will be just my husband and myself going in early may. I am aware of the weather so plan to be prepared. We also like the local tours. I will look into these regardless of having a car or not. I may rethink some of our trip after reading your tips. We have a limited time in Scotland (12 days) so saving some and frustration is important. Thanks again.

Think about flying there and then taking the train back south. :)