Assuming that the product is just what it says it is - 7 places you might hear tales of if you chat up the crowd at the Yawning Portal one night, with the theme being dungeons - I would personally make additional volumes in the hypothetical series also incorporate other themes.
Like one volume containing specifically castles you might hear of, and another containing specifically strange wilderness sites (like where another plane of existence spills over into the material just enough to cause not-quite natural geology). Of course, reserving the right to return to any of the themes of these locations with later volumes.
It would take me months to decide for sure which theme I'd do first, and which sites I would choose to fit the theme.