Probably my favorite module in the great and prestigious long-running line of supplements, Th Mysterious Tower is a great old school-styled adventure that I have run with many of my groups for greqat effect and hours of enjoyment. While it 's aimed at low-levels, it can be easily scalable for Joseph made a well thought-out series of plans a nd encounters that can be easily adapted to siut your specific player groups.
While it's easy tu run, it's by no means straightforward, and with careful scheming of the DM's part it can easily keep the players on their toes and thinking their way out of increasing trouble.
Finally, I must admist that 3e wasn't my cup of tea, but the best thing with every Goodman Games module is that it can easily be adaptyed to suit your group's playing style or the system you've chose. So, yes, it will work--and marvellously so--with Pathfinder and be very easy to transplant into any of the newer Rune Quest settings... or go real old-school and use your AD&D or AD&D "nd Edition rules with it, with minimal hassle.
All in all, a solid, easy to read and use module from Goodman Games. I heartily recommend it.