Well, thanks to you guys I managed to download correctly a Sandbox Park.
Now, I go to the main menu > Sandbox > Load and select my downloaded park. I wait for it to load up but there is nothing there, just a blank wasteland; I'm unsure of what to do?

Do I just leave it, is it loading?
Do I need expansions?
Is it just a really bad park with nothing there.

I cannot even see the entrance or any peeps.

Thanks,
Kazil.

I had it once as well,

I'ld suggest re-downloading the park, and else, look for an e-mail of the author/maker/creator of the park and ask him

Thanks, I took your advice and it works :P
I owe you one.