Gravity has been running the Yungas road since 1998, which means they were selling the descent before it was a backpacker rite of passage and before the new highway took the traffic off it. That matters mostly because of what it has taught them about brakes, guides and the weather on the 3,500-metre drop from La Cumbre to Yolosa.
A day costs $140 and the group is capped at fourteen. They also run a much longer list than the one ride everyone comes for: the Takesi and Choro trails, singletrack above the city, a multi-day Sorata loop and an Illimani traverse.
The office is upstairs at 940 Linares, between Sagárnaga and Tarija, open weekdays 10:00 to 18:30 and closed at weekends — which is worth knowing, because you will probably want to book on a Saturday.