The main ferry to Orkney is the NorthLink service from Scrabster (near Thurso, on the north coast of the Scottish mainland) to Stromness — 90 minutes, several sailings a day in summer. NorthLink also runs an overnight ferry from Aberdeen via Lerwick (Shetland) to Kirkwall.
A second, cheaper, foot-passenger and car ferry runs from Gills Bay to St Margaret's Hope on South Ronaldsay (operated by Pentland Ferries). In summer there is also a passenger-only fast ferry from John o' Groats to Burwick.
By air, Loganair flies to Kirkwall Airport from Edinburgh, Glasgow, Aberdeen, Inverness, and Manchester. The airport is six kilometres south of Kirkwall.
Once on Orkney, internal ferries (operated by Orkney Ferries) link Mainland with all the inhabited islands. Loganair also runs domestic inter-island flights, including the famously short Westray–Papa Westray hop.
A car is a substantial advantage, especially for visiting Skara Brae, the Ring of Brodgar, and the more remote parts of Mainland. Otherwise, allow time and a bicycle.