Carlsbad is big, but there are bigger indoor spaces out there. Carlsbad's "big room" is 625 ft wide, and 255 ft high at its highest point. That is big, but things like stadiums get bigger. Carlsbad is long too (4km) but as a cave length isn't really perceptible. NASA's vehicle assembly building is 720 ft by 520 ft and 530 ft high, roughly the same but much higher than Carlsbad.

Tropical Islands Resort is a tropical water park (Germany): 690 feet wide and 351 feet high.

https://en.wikipedia.org/wiki/Tropical_Islands_Resort

https://en.wikipedia.org/wiki/File:Tropical_Islands_Halbe_14...