There are a score of tour agencies and adventure tour companies in and around Mérida. You'll find the greatest congregation of them around the Plaza Las Heroínas. The competition is cutthroat and you can often find good deals by shopping around. However, be careful, as some of them are fly-by-night operations. I highly recommend the companies mentioned, as their level of service, quality of guides and equipment, and safety standards are consistent and dependable. Whatever tour company you choose, be absolutely sure that you feel confident about the competence of the guides and the quality of the equipment.
Arassari Treks, Calle 24 no. 8-301, behind the teleférico (tel./fax 0274/252-5879; www.arassari.com), and Natoura Adventure Tours, Calle 24 no. 8-237 (tel. 0274/252-4216; www.natoura.com), are the two most established and trustworthy tour companies in town. Both companies offer most of the outdoor adventure options listed, and then some. Both can help you with onward tours and trips to Los Llanos and most other destinations in Venezuela.