We got a bit restless staying on our all inclusive resort all week, so I found a man on the beach who set us up with a cab to Mayfield Falls. Seemed sketchy at first, but turned out awesome. Cab driver was named Everton Banton with Juta Tours, and I'd highly recommend him! He answered all of our questions and gave us interesting information along way.
We stopped at a fruit market in Savannah La Mar on the way and got the best fruit we had the whole trip---it was interesting to see the market also because we were the only tourists we saw there. Great detour.
The "falls" themselves are not really a waterfall, but more of a mineral spring (think river) you walk through, so don't expect breath-taking waterfall views. That being said, Mayfield Falls was gorgeous--set back in what feels like a tropical jungle and so peaceful. The water was cool and refreshing and the walk itself is entertaining--areas to jump/swim/play. The walk took between 1 and 2 hours total and was not extremely physically demanding (I'm fairly physically active and would not call this a workout by any means), though there are some stairs on the way there/back and you're walking along a rocky river bottom, so it could be difficult for someone who has trouble walking We left our stuff in the lockers-no problems. Also, it's pretty much entirely shaded, so don't worry about sunscreen.
They have tour guides available for free (they expect a tip at the end) when you arrive, and the cost to get in is $15 per person, plus $6 to rent water shoes (you'll actually be glad you did). They also send a photographer with you and you can buy the pics at the end if interested.
I'd definitely recommend this little excursion to anyone--it's peaceful and beautiful and the drive (while slow going and bumpy) is a good way to see a little more of the island.