It is hard to find good swimming holes in the desert, so they are all precious. At the end of the Babylon Arch Trail (about a mile and a half each way) is a sandy beach on the Virgin River just northeast of St. George, Utah. The town of Leeds has far fewer people, so this one is a bit of a hidden gem. The hike is fun and not too difficult, and it is definitely worth the trek. There are some cool alcoves along the sandstone, and there is a section of river that is deep enough to get fully into the water. The best time to be here is in the spring because the water can get pretty low in other times of the year unless it has rained heavily recently nearby. You can bring your dogs, but make sure the hike is not too hot or far for them. You can also camp, but only at the Sand Cove Primitive Camping Area about a half mile into the trail and a mile from the river. Reserve the free permit for that here. The river is long enough here to hold a lot of people, but chances are you won't see too many.
The dirt/rock/sand road from Leeds to the trailhead is usually passable with two-wheel drive unless it has recently rained, in which case you will want four-wheel drive.