The Encierillo, or "little bull run," is a quiet event in which the bulls and the oxen are led from the Coralillos de Gas, named after a 19th-century gas factory that was converted into a bull corral, to the Santo Domingo corrals where the bulls spend their last night.
The event involves about 400 meters of nocturnal bull-running, without any lights except the usual street lamps. Although there is no fixed time, this event takes place around 10pm on the night before each bull run. The ambience of this event is tranquil and highly respectful, and the running takes place in silence while a limited number of ticketed observers watch from behind barricades. Watch a video of this event here.
Tickets to this event are very limited and very difficult to obtain - they are won by lottery, so you won't be able to make reservations in advance. However, you can get a view of the bulls once they reach their corrals in Santo Domingo from the top of the wall of Santo Domingo. Take a break from partying to walk to the lookout spot on Santo Domingo any night between July 6-July 13 and pay respect to the bulls.