Hari's Horses in Merida, Altagracia are the best horses I've seen on the island. The best way to really visit Ometepe is on horse back. Hari is german and his horses are all healthy, well fed and shod. I went for a full day ride, started in Merida at the feet of the Madera vulcano and visited all the beaches from Santa Cruz to Altagracia running and splashing on the lake front. Lovely day and lovely experience. Hope to go back soon!!
Equipment: I advise to have a full day excursion, start early, wear long trousers and enjoy yourself!
Ride towards the horizon on one of the many horses at the Finca. They rent horses at very reasonable prices by the hour with or without a guide. Excellent way to explore the island!