I went to the Riyadh Zoo yesterday and thought some of you might be interested in going, too! Was very reasonable admission: 10SAR for adults and 5 for children.
There wasn't a huge selection of animals to see (not like the very large zoos in other capital cities I have visited); however, the park was large, uncrowded, clean, green and nicely landscaped. I saw that many smart people had brought coolers and after touring the zoo, settled down in the grass in the shade, ate lunch and enjoyed the outdoors.
Yesterday, Thursday, was family day, so single women and families were there. I'm not sure which days are for single men or if the days rotate so if you're a single guy who wants to go, better check with zoo first.
If you want to see the pics of the place, I've posted them on my profile.