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.
The first visit was a bust (March 2010) due to the flooding of the Suwannee. Apparently this happens fairly regularly, so be sure to check ahead to make sure the Springs are open and clear.
The second visit was a pleasant surprise and did not disappoint. I sort of forgot that the park was maintained/owned by Gilchrist county (and thus had an entrance fee), but my $4 was well worth it a few minutes later. The facilities for changing were very nice, and the concession stand wasn't half bad either! With two vents, even the number of people didn't deter me from hopping in and going for the more-eastern vent. While a little scary being all alone in the pool surrounding the boil of this vent, the depth was extraordinary. I was able to dive a good 15 to 20 feet before reaching a horizontal cave gushing clear water. Visibility wasn't great due to all the vegetation, but I'm not sure why the spring showed so little use. I was pleased.
Rather than exit at the beach and walk to the other vent, I chose to swim the gap. Visibility in this area wasn't quite up to what I expected, but it was mostly due to the crowds and sand being kicked up. Swimming a few feet under the surface gave me a better if darker view, spotting many schools of fish darting around unsuspecting visitors. After a quick breath under the bridge I arrived at the pool for the second vent.
I see now why it was more populated and fresh: the walkway above the sharp banks opened a tiny bit to allow jumpers access directly over the boil. It was more difficult to swim in this area due to that fact, but the clarity and force of the water made up for it. Check out the photos below for July 2010; the clarity of some of the later shots is amazing.
A boardwalk takes visitors out to the Suwannee which flows by just a quarter-mile from the springs. Had the mosquitoes and heat not been as bad I may have snapped more shots, but it is nice to take a step away from the crowds and see a seemingly different ecosystem.
Overall, Hart Springs surprised me. I think it's only downside is its location: fairly far from I-75 for hoppers from the east. However, if you ever end up in the High Springs / Suwannee River area, stop by. Just make sure it's in the summer!
This spring was so nondescript that I don't even know if I could point it out directly. Not worth it.