Cat and Thomas Mountain loop, containing two of the Lake George 12ster peaks, is a fun and beautiful loop with rewarding views at both summits. The section headed up Thomas is short with a steady climb. The route up Cat is wide, rocky and hardy, and the backside trail between Cat and Thomas is more gnarly and remote. A fun mix of everything! Note there are two ways used for the descent - this is due to new trail vs. old trail and doesn’t appreciably change distance so you can choose either.
For the record, the original route begins from Valley Woods road and parking lot. The true summit of Thomas Mt. is unmarked and off trail, and is not recognized as part of this run. Thomas mountain viewpoint, which used to have a really neat cabin before the DEC had to demolish it in 2017, has a beautiful view and is recognized as the high point on that trail before descending toward Cat Mountain.
For reference, here are links for the Lake George 12ster challenge, and the Lake George and Conservancy.