Walking around inside a drawing of a house

I have a Sketchup drawing of our future home provided by a local designer. I can view the outside, including top, and even underneath. However, I have not been able to view the interior of the home. I have explored several options. the “walk” option is grey and cannot be selected. Is there a way to go inside my drawing and explore?

If you open the file in SketchUp Free instead of SketchUp Viewer, you can use the walk function and many more functions.
You would have to create a Trimble account but it’s free…
Go here: https://www.sketchup.com/products/sketchup-for-web

Probably the camera is set to parallel projection.

Thank you! I switched to “perspective” and I was able to move into the house and look around.