Of the first two-day jaunt, this was probably the most stunning all-around. I don't know if words really work to describe how it shined in the morning; the pictures below do it much better justice.
The park is technically a state park but is maintained by the SRWMD, so there's no visible staff or complex facilities; this probably went a long way to preserving some of the fun of the park. The spring has a direct-access jumping platform and a dock; paths are made of mud and roots, not concrete; there are no ropes to be found in the swimming area. The spring run snakes around a small limestone formation and into the Withlacoochee river, crashing over a line of rocks into the tannic water.
This spring has everything: cave diving, free diving, deep swimming, shallow areas, wading areas, relaxing rapids, river wading, and fishing. My only regret is not swimming. We were in a hurry and it was the first spring of the day, but I do very much regret it. Madison Blue Springs State Park is highly recommended, and I cannot wait to go back someday.
The spring itself is actually about 10ft lower in elevation than the hiking trail, so you'll have to scale down (and up) some fairly sharp clay and sand inclines to get to the spring itself. There is a walkway that appears to have gone down to the spring at one point but the bank has been washed out, making it useless to access the spring.
It's a very pretty spring, although it's very small. It's only about 20ft from the Suwannee, so there's very little if any opportunity to swim. The water falling over the limestone "cliff" is still very cold so perhaps there's an opportunity to swim in that larger area. Cypress trees grow out of the side of the area so look out for the plethora of cypress knees in and around the spring.
I have to say, it's a lot of work to get to this spring, and I don't know if it's worth it. You have to pay to enter Suwannee River State Park, then park at the boat ramp, then walk a good 5-10 minutes, then scale off of the trail to find a spring that you can barely enter and more likely will just observe.