Again thanks for the directions. I visited the bike rental place in the Mirador del Sur, above the tunnel of the Nu?ez de Caceres, and the bikes looked like simple, slightly rusty mountainbikes, but adequate for a spin in and around the park. Most are in children's sizes. I wasn't able to use their business though, because in true dominican business sense they are closed during the week, and used most of saturday to 'clean the bikes', and it was absolutely not possible to rent one. But, they're still in business, and if they're not cleaning them you can indeed rent a bike there during the weekends.