BA codeshare with Loganair on the leg to Lerwick, e.g. from Aberdeen.
https://flights.app.goo.gl/pXeH1
If Gold, I believe you get lounge access in ABZ before you Loganair flight, as long as you are booked on a BA flight number on a BA issued ticket.
Doesn't seem a partiularly cheap place to visit:though and you can't redeem Avios on Loganair flights, snce they dropped the partnership with FlyBe (and FlyBe stopped using Avios anyway).