Up past Skaill Church take a left at the very next junction, a farm road that takes three sides of a square that brings it back to the proper road again. On the first side is the farm track down to Lenahowe. Here is the Linnahowe Mound just as advertised by the NMRS, a long prominent mound occupying most of an enclosure, many stones revealed by the pit but nothing resembling any kind of structuring. I only saw a few stones in the undug bit, nothing you could make anything of in the slightest.
Marwick ("The Orkney Herald" 11/7/1888), rather fancifully, in my opinion, asserts that Linahowe means "the goddess of love and marriage". He records that local tradition says the Church of Rome sent a priest called Mohr to the Bay of Skaill to convert the pagans, and that he set up a church near by Linahowe.
Brand 1703 "the Minister of Sandwick's Manse is said to have been the residence of one of the kings of Picts... to this day called Koningsgar or the King's House... tho now kept in some repair... The figure thereof and the contrivance of its two Rooms or Chambers one above and one below, of narrow dimensions, and antick, and the Building hath been but coarse."
In a book on the Breckness Estate there is a quote from 1830 of "a mound of stones on the sea beach, called the Castle of Sneusgarth" which means the castle is either this mound or (more likely) the broch [unless there was a now lost mound at the taing]. The castle is a moveable feast whichever way you read things.
The other side of Skaill Church from the Castle of Snusgar. 'The Castle' was an old structure now gone to leave behind a detail-less spread of stones in an extensive mound. A silage pit dug through one end uncovered no evidence of walls amongst the stones but did find ashes and old bones.
On analogy with why the brochs of Burray were locally differentiated as "Hillock" and "Castle" it appears that the latter name is used for sites with subterranean chambers ("dungeons").