It being a chance at a chance for extra loot is potentially a bit disappointing, tbh. It largely depends on how high the % for the Aquapolis portal spawning is - if it's frequent enough then you'll at least get to go in there often and getting to the end of one won't take you that many tries. If it's a low % chance, however, then that's going to be less fun and more aggravating grinding just to get in there to then attempt to get to the end if you're lucky enough.