From publisher blurb:
'The City Out of Space' is a quick-adventure for a party of four 5th level characters. Very little adaptation should be necessary to use in any campaign setting.
Encounters, Treasure, and other system specific information can be found in the compatibility packs freely available with this adventure.
Adventure Background
Ashland is a large city with a diverse population located at the heart of a trade center. Impressive in both size and population, Ashland is the largest city within a week of travel by horseback.
One morning, as the sun touched the city at first light, there was a shimmer in the sky. Over a bit of time the strange shimmer became more and more clear. More and more it began to seem like a city... floating above them and mirrored. So far away it could not be seen in detail, but most everyone agreed it looked much like Ashland.
The City Out of Space appeared out of nowhere, and has remained floating above Ashland for days. Nothing dangerous has come from it, but everyone is gravely concerned. Especially the local government, who has sent out a call for experienced adventurers to explore the city and answer their questions.
Depending on your campaign needs you can change the city identity to one local to your campaign setting, and change the methods of getting to the city as appropriately. By default the players are assumed to have been given a method of flying to get there. Whatever means they have the players will approach the city in the same place.