If you are staying in Manuel Antonio you may think that roads are rather flat around there and they are. It's a great location for Triathlon and Ironman training as you can cycling over 200KM on flat roads with small rises and dips. However if you cycle around 50km to Dominical (great warm up), take a left as you enter Dominical then you start to climb for 26km towards San Isidro de General.
This ride is a beautiful ride that is best ridden early in the morning so that the roads are quieter. The ride from Manuel Antonio to Dominical will take around 90 minutes which is a great warm up, then the 26km climb will take another 60-90 minutes depending on your fitness level.
The views during this ride are stunning as you first go through palm plantations and then as you climb you see beautiful sweeping valleys that are lush and full of wildlife. There are also many restaurants in the area, so feel free to stop and taste some of Costa Rica's finest coffee.