Signhildsberg

Signhildsberg (historically Fornsigtuna, where "forn" means "ancient", Old Sigtuna, "Sithun", "Signesberg") is a manor that formerly was a royal estate (Uppsala öd), located in the parish of Håtuna approximately west of the modern town of Sigtuna, by Lake Mälaren in Sweden. Although the location is nearly forgotten, it has a central role in Norse mythology, according to which it was founded by the Norse god Odin. 
Etymology.
The name "Sigtuna" is contested. According to one theory, it is a compound name where the second element is -"tuna" and the first one is either of two closely related dialectal words, viz. "sig" meaning "seeping water" or "swamp" or "sik" meaning "swamp". As a basis for this intpretation, a brook south of Signhildsberg has been mentioned, or the fact that the estate was surrounded by marshy terrain. 
Another theory considers the name to be an ancient prestigious "wander toponym", meaning "strong fortress", like the Celtic toponym "Segodunum", from Proto-Germanic *"sigatūna"-, Old Norse "Sigtún", cf. Proto-Germanic *"segaz ~ *sigiz"- "victory": Gothic "sigis", Old Norse "sigr", Old English "sigor", Old Frisian "sige, sīge", Old High German "sigi, sigu".
In 1680, the name was changed to "Signhildsberg" after the Old Norse legend of Hagbard and Signy.
Heimskringla.
In Chapter 5 of the "Ynglinga saga" section of his Heimskringla, Snorri Sturluson relates that Odin and the Æsir first arrived at Old Sigtuna when they came to Sweden:
Later the pirate Sölve arrived at Old Sigtuna to claim the Swedish throne: 
In the part called "The Saga of St. Olaf", the Norwegian king Olaf Haraldsson makes shore at Old Sigtuna:
Skaldic poetry.
In "Orvar-Odd's saga", Hjalmar laments his dying:
The location is also mentioned in other poems by the 11th-century skalds Þjóðólfr Arnórsson Valgarðr á Velli and Arnórr Þórðarson.
"Gesta Danorum".
Saxo Grammaticus writes in Book 8 of "Gesta Danorum" that Sigmund, one of the warriors of the House of Yngling, came from what is chronologically Old Sigtuna to fight at the Battle of Bråvalla:
Archaeology.
There are two large ruins that had been two large three-aisled halls, a series of terraces just above the shore-line of the Germanic Iron Age, traces of a harbour, a large mound and a number of smaller grave fields. Excavations have dated the remains to the Vendel Age, part of the Germanic Iron Age, and the Viking Age, i.e., from the 6th century until the 11th century.
History.
It was an Iron Age and mediaeval royal estate (see Uppsala öd) and it was located strategically at the waterway to Old Uppsala and the Temple at Uppsala. In the 10th century, the name was transferred to modern Sigtuna, which apparently assumed many of its functions.
Since the 17th century, the location has been a manor named "Signhildsberg" or "Signesberg".
Other Sources.
Nationalencyklopedin and A historical review of the name, from which the information about the name and dates is taken.