I've often wondered about the Excelsior hanger bay, seeing murky blue shapes inside in the closing shots of STVI and elsewhere, but only recently did I find these awesome shots of the actual Excelsior/Enterprise-B/Lakota model:
So what is this? It looks like some sort of freighter parked inside. The bay also appears to be open to space.
Here are many more pics of the model (and other Trek ships) here: http://www.modelermagic.com/?p=2932
Also, looking at those tiny windows and that miniscule bridge dome (with windows around indicating surrounding rooms NX-01 style, and a lounge behind Enterprise-D style), the Excelsior must be far bigger than it's supposed 467m. We're talking 750+ meters.
Awesome model, btw