Question on making structures

Okay so I've been wanting to build a themed viv for my dragon. I'm mobile atm so I can't easily throw reference pics but I will once I get home tonight. I'm wanting to build a Sovngarde themed tank because in Skyrim, that's where Alduin lives basically, and my dragon's name is Alduin. I'm wondering if it'd be safe to make the structures like those in Sovngarde or if I'd have to make em more natural. One of the structures is a whale skeleton, and it's a bridge so I'm not sure if that'd be okay in terms of safety. My main question here is what supplies are safe and cheap? Don't worry about how easy or hard it is to make them, I've got my skill set in place for this lol. I'll post pictures as soon as I can as well as a sketch for what I'd like to make. Thanks!

Edit: Here are the pictures for reference.
Whale bone bridge & Hall of Valor in the background:

Another one:

Hall of Valor:

That looks like it may be pretty difficult, but assuming you have the tools (or access to someone who does) you could probably make that bridge out of wooden pieces. It would probably make a nice climbing area as long as you keep the edges rounded. You could make that background out of wood too, or you could just print out a large format photo of it and put it up as a background image.

A frame of wood would make it stable and you can use expanding foam to make/carve the shapes. The foam can be covered with grout or something like sand imbedded in silicone. Sealed properly the materials would be safe.

Alternately you may have luck browsing in eBay or sent hug for actual bones.

One thought though - depending on how big it is the shapes may not be very comfortable for a dragon.

I have some experience with wood, and my stepdad has many tools that I can easily use with his permission and guidance, so that's not a problem. I've been wanting to make the whale bone bridge rather rounded to make it safer for Alduin to crawl across and not worry about accidentally impaling himself. It'd be heavily modified but you'd still be able to say "yea that's a whale skeleton." I'm always worried about keeping my boy safe haha. I'm considering printing out the backgrounds too, but I'd like the interior to at least have something related to Sovngarde, but if not, I'll make do. I'm rather iffy on bones because it could crack and may eventually go rancid or whatever, but that sounds like a cool idea nevertheless. I can't remember the dimensions of the tank, but I believe that I could make it roomy for him. I'm thinking of making the bridge high enough so he can crawl under but not too high so he wont burn himself while basking. The Hall of Valor would have a hole somewhere (I haven't decided on where) so he could go inside, and I'm gonna measure it so it could be big as I can comfortably fit in the tank. The rest would probably be a platform on the warm side with a statue or two on the side with a cave underneath it, like a really big cave. Then the center/front area would be rather flat, allowing space for food to sit in a bowl. I have yet to draw up a sketch of it though. I'll try to get to that tonight.

The sealed foam is a good idea too. That'd probably be pretty easy to shape. What I had in mind with the wood structure is something similar to the wooden dinosaur skeleton kits that are around (modified a bit) to get what you're looking for. Something like this

Dude that's a fantastic build to go off of! Thank you for sharing that!