The zipline tours through the forest canopy originated as a commercial venture in Monteverde. There is some dispute about by who and how they were invented. One of the local businesses even has a copyright on the term "canopy tour", which has become the catch all term that many use to describe this adventuresome activity. We won't get involved in this argument.
But we will tell you that this is one of the most fun things you can do during your adventure in Costa Rica. They are scattered all over the country. But I feel that the best ones can still be found around Monteverde. There are some slight variations on the mechanics. But all are basically long cables stretching from one hilltop to another. The participant (that would be you) wears a harness, that was borrowed from rock climbing gear. There is a pulley mechanism that fits over the cable, and this attaches to your harness. You stand on a platform, lift your legs, and let gravity take over.
Soon you are flying through the trees, and over valleys, sometimes several hundred feet up. You can get moving a pretty good clip too. There are guides with you constantly, to assure your safety. They help you get your gear on, and hook you to the cables. They are there to stop you at the end of each run. Sometimes, the platform is high up in a tree or on a tower. In these cases, you are attached to a safety line before you are released from the main cable. The pulley system itself has some redundant safety lines too. So this activity is a lot safer than it first appears.
It is not for the faint of heart, or those with a fear of heights! But it is exhilarating and lots of fun. The typical tour will have at least ten platforms, sometimes more. As each new tour opens, it brings improvements. So the established tours scramble to keep up. I have heard of a Central Valley tour that offers a long "superman" style cable. Here, you lay straight out and face down. The cable is above, so you fly like Superman. Sounds great. At least one Monteverde operator has added a "Tarzan swing" as a side attraction. They hook you up to a swinging bungie cable. You free fall about ten feet, and then take a long lazy swing out over a little gully. it is scarier than it sounds! But still fun.
The zipline tours are meant for all ages, as they really are not that strenuous. Obviously, the littlest kids are not going to be allowed. But I have seen kids as young as five years old on the tour. They usually ride double with a guide. The cables are very strong. A guide once told me that they could support a car. But some do have weight limits, that will restrict the largest folks. So if you think that this may be an issue for you, it is best to check ahead of time.
Two of the Monteverde tours also offer bridges and walkways through the cloud forest canopy. This is a great place to walk with a guide or by yourself to see what you can spot in the treetops. It is also an option for the less adventurous to enjoy while the family daredevils are on the cables. One tour operator has expanded into a full blown nature park with butterfly and hummingbird gardens, insect exhibits, a reptile and amphibian exhibit, and a full restaurant. You can enjoy a whole day here, and never leave the grounds.
One last thing. Some of the tours offer this up as a nature experience. Other than the pretty woods, this is usually not the case. The hooting and yelling tourists tend to drive the animals away. But let's be honest. You will be standing on a platform and attached to a cable, preparing to speed high over the treetops to a destination that you may not even be able to see. Are you really going to be thinking about birds and flowers?