Old mud villages are everywhere in Saudi Arabia. The first restored section of Diriyah should be opening in a few months and if you drive in pretty much any direction, you'll find a town with an old mud section in varying states of dilapidation. They really weren't abandoned all that long ago but these buildings need constant maintenance so they fall apart quickly. They're a bit like ghost towns.
It seems that you can go poke around these places whenever you want to and no one minds. Historical preservation in general isn't a major priority here and no one owns the buildings. I love going to these so I've been suggesting for a while that we go to Ushaiger because the people there have restored part of their old town and it sounded interesting. And it was.
There are several museums and restored homes that open for tourists, especially tour groups. We were there on a weekday morning so nothing was open except the main museum. If you go, try to budget some extra time for tea and chatting with the man running the place. He loves it. But other than that, you can wander wherever you like. There are larger homes, several mosques, squares and courtyards and nicely paved streets, and farms and fields and wells around the edges. We spent a couple of hours there without seeing everything, but I want to go back with some of the boys because I think they'll like it too.
It's just two hours from Riyadh. You can go northwest out of the city or down the escarpment and north from the first exit toward Dhurma. Go one way and return the other. It's also a nice way to see the escarpment.
In some of the photos below, you can see a restored home with a spot where a fire could be lit inside, plus ruined versions of the same thing.