Please help honestly not sure even how to describe?

Hey all so last night I went to Hide everything except the gym when i unhid everything seems to have turned to this mesh ? please help thanks

You need to be careful using hide, it’s really just for a quick hide and unhide to temporarily get something out of the way. Hide is context sensitive, so you can hide lots of things in different groups and using Un Hide all won’t unhide them all, because you may not be in the correct context.
But looking at your screenshot what you are seeing is some hidden objects and some hidden geometry. The white grids are hidden objects and the other mesh lines on everything else are the actual ‘hidden geometry’ that makes up everything and needs to be there.
If you go to View and untick hidden geometry, the dashed gray lines should disappear and the white grids should stay. It’s the white ones you need to select and unhide, you may have to open them and unhide their contents.
Seeing your model would make it easier to answer specifically.