On the border of two counties is Loch Leven, where Mary Queen of Scots was once imprisoned, and home to the longest, most accessible walk I have been to. The heritage trail around the loch is 13 miles (21 kilometres) in length and totally do-able for powered wheelchairs, scooters, and walkers who struggle with inclines - it Is completely flat all the way round apart from a little stretch near the bird sanctuary.
There are a few different carparks around the loch to start your walk from and I'd recommend two of them from an ease of access point of view, either at 'Loch Leven's Larder' or Kirkgate Park in Kinross. Both of these locations have large carparks with disabled bays and are at opposite sides of the loch, so you can change it about if you decide to visit more than once.
Loch Leven's Larder is a large modern farm shop and café with lots of indoor and outdoor seating for when the weather is a little better, and it also has an accessible toilet. You can also hire out an electric scooter here, just speak to somebody behind the desk in the shop. There are only two scooters available to hire so it may be worthwhile phoning up and pre-booking. The number is 01592 841000. Behind the farm shop/café there is a large cricket field with a path running along the side of it leading down to the beginning of the trail. You can either turn left or right (I turned right).
At the Kirkgate Park side of the loch, there is a large play-park for kids (there is no equipment for kids in wheelchairs) as well as plenty of green-space with views across the loch (and the prison where Mary Queen of Scots was held captive) - it is perfect for picnics. There is also a block of toilets halfway up the carpark, you'll need a radar key to use the accessible toilet.
By turning right and following the path past the small harbour, you will begin the next stretch of the walk, and behind the buildings at the harbour you will find another toilet block - I would recommend using this one rather than the other. This path eventually takes you past RSPB Scotland Loch Leven and the Findatie car-park, which is where the final section of pictures in this post begins.
This is the toilet within the carpark.
This is the other toilet block.
At the Findatie car-park you will find the Loch Leven Lodges and its coffee shop. Great for a little refreshment and it has an accessible toilet. Only negative about this pit stop is that to reach it from the walking trail you need to go up a steep hill.
The path up the hill is a good enough surface and it should be fine for electric wheelchairs and scooters but just pay attention for any bumpy bits. The levels of the gravel path can be easily manipulated by heavy rainfall.
Obviously you don't need to walk all the way round, you can just do a little stage of it and come back another weekend and do a different bit, and whatever you choose you will have a great day out. This walk is one of my favourites and the length of it is a bonus.