From Tatters of the King
In early December 1928 a cult lead by Montague Edwards, with the assistance of Alexander Roby somehow brought Carcosa physically to Earth. The city invaded this reality in Scotland, appearing on the shores of Loch Mullardoch which apparently became the lake of Hali.
1. It appeared overnight.
2. One could not tell from looking at it whether the city sat upon the waters of the lake, or beyond them.
3. When the moon arose, the towers of the city appeared behind it, not in front of it.
4. As soon as one looked upon the city, one knew its name
5. Unknown, but has something to do with the 'mystery of the Hyades'