That soo wacky, but great that you got there! <img src="/images/graemlins/smile.gif" alt="" />
The Hollow Bastion was pretty cool and very intricate with a lot to do. You can get to the Grand Hall by entering the Lift Shop and going up the stairs. Below are the puppy locations. Have you been periodically going back to visit Pongo and Purdy? I think the castle gates are the place were you either first end up when you warp or just after you ride over to the castle. In any event look for a floating check..:) Good Luck!
Hollow Bastion
61, 62, 63: In the Grand Hall, accessible the second time you visit here.
91, 92, 93: Bottom of the Rising Falls.
94, 95, 96: Castle Gates, cast Gravity on the floating chest.
97, 98, 99: High Tower, cast Gravity on the floating chest.