Riverview won't download.

@Weltato  You can only download store content, including Riverview, if you're signed into an account on the Sims 3 Store site, and of course if that account owns a copy of the game.  I think you need a valid product key to create an account on the store site, or else you need to use the login credentials from an Origin account that owns the game.  So if you've never been able to register your copy, then you may not be able to use the store site.

There are plenty of player-made worlds on various other sites.  Some only use the base game as well, so you may be able to find some you like.  They install just like store content, as in, through the launcher, but they won't be encrypted like store items.

It's a good idea to check out any downloaded content in a clean Sims 3 user folder though, just to make sure you don't get any extra custom content you don't want in your game.  If you move the Sims 3 folder out of Documents\Electronic Arts and onto your desktop, a new one will spawn the next time you open the launcher, and you can install whatever you want into that folder.  Once you're satisfied, trash the new folder, put the old one back, and install the ocntent you'd like to have.