Corel Dream is an older version of Raydream Studio. Unless they've made a lot of changes I don't know about, the 3DMF files would have to be in .t3d, .b3d or the same .3mf filter that's used in Poser. 3D Exploration does indeed read some files with the 4 digit extension, but not the ones from "Great Buildings On Line".

I'd rather stay in my lane than lay in my stain!