I got some questions (off-page) about the labyrinth in Fröjel. There are a few more on Gotland, among them one in Bunge that we visited in 2004. But instead of writing more on Swedish labyrinths, I decided to find out more on the Norwegian ones. I already knew of one on the small island of Tisler in the Hvaler archipelago, but more on that further down.
The Norsk arkeologisk leksikon, 2006 (title translates as Norwegian Arceological Handbook) says that labyrinths as a symbol is known from petroglyphs (norwegian helleristninger), in churches from the Middle Ages and as stonesettings.
In Norway they are most common in Finnmark, as part of a larger cultural area including Kola and the White Sea in Russia. They are usually situated close to graves and it is assumed that they were used in passage rites.
In southern Norway, several petroglyphs with a labyrinth-motive is found. Labyrinth-stonesettings are found in Sunnmøre, along the Oslofiord and southwards along the Swedish Bohuslän-coast. Labyrinths are sometimes called Trojaborg or truberborg.(All the above is taken from Norsk arkeologisk leksikon page 233.)
On Sunnmøre there's one stone-labyrinth known as den Julianske borg (the Julian castle) on Vartdalsfjellet (Grøthornet) in Ørsta.
In my local area I only know of one stone-labyrinth. It's on the (very) small island Tisler, on the east side of the Oslo-fiord. Only parts of it is still there (there's traces of another close by). It may be as old as 3000 years, but that is guesswork. Tisler is not easily accessible, it is only possible by boat in (preferably) good weather. The labyrinth lies on the north-east part of the island on a small hill called Slottsfjellet (eng. Castle Hill). I have never been to Tisler, even though I have spent many summers on an island not very far away. Morten Kiellands report on the proposed national park in Hvaler and Fredrikstad has a picture of the trojaborg:
Of the several located in Finnmark (the northernmost county in Norway), I have only been able to find information on four, one on each of the islands Holmengrå and Kjeøya. According to Samitour there are labyrinths at the mouth of the Tana River and one in Magerøysundet as well.
The name truberborg seems to be taken from a (now lost?) labyrinth on Østerøya in Sandefjord. The place is called Truberodden (Truber Head or Point). I had not heard about Truberodden before starting looking into labyrinths, as it is not far from where I live I definitely will take a look soon.
According to the Bergkonst-site Norsk arkeologisk leksikon is wrong when it says that there are petroglyph-labyrints. A petroglyph from Tanum, Sweden (from the link above) has labyrinth-looking motives: