This doesn't seem to be working today - all black screen
For me it works normally and last time it was updated more than a year ago, so it's not like I uploaded something broken recently. All these WebGL applications (City Viewer, Procgen Mansion, Castle in The Mist) are pretty unstable and sometimes they stop working without obvious reason and there is no way (or I don't know how) to fix it. Usually restarting the browser helps.