On the Las Juntas -> Santa María route, you will cross 14 tunnels that cross the Eastern Cordillera of the Andes to reach the Piedemonte Llanero. If you go in this direction, most of the route will be downhill.
The longest tunnel is 1640m long and the shortest is 90m long.
It is essential to bring good lights and a reflective vest as the tunnels are not illuminated.