Pacaya Volcano is the most frequently climbed volcano in Guatemala. It is relatively easily accessible and commonly puts on a good show for volcano enthusiasts. Pacaya's current active phase began in 1965, and the volcano has been almost constantly in eruption since then.
There are many tourist companies that offer daily trips to Pacaya, especially in Antigua. You may want to consider this option if you would like to see Pacaya at night.
If you have access to a vehicle, leave the capital heading south on CA-9, the highway to Esquintla. Turn off on the road and head toward the town of San Vicente Pacaya and Pacaya Volcano National Park before reaching the town of Palín. Watch carefully for the sign...it's not very prominent.
The road up the mountain to San Vicente was paved in 2001. But from where the entrada to San Vicente forks off down to the left the road continuing straight on up through the village of Cedros to the hamlet of San Francisco de Sales and Pacaya Volcano is dirt. It is rough, but passable all year round, unless blocked by a landslide or mudflow. Once in the village, there are many places to park your vehicle.
From San Francis de Sales (1883mts) the trail follows a well defined path in a southerly direction. The initial part of the trail is paved with stones. At about 1963 meters, the trail branches off in two directions. Take the south/southeast branch. The trail continues in a southerly direction for some time until you reach about get to about 2120 meters. where you will find another split. Take the SE branch. Continue on this path for some time. You will pass a large open space (2130 meters) with a huge oak tree (see images below)in the middle. Just past this spot the trail splits again. One path, to the right, leads to a vista with a view of the cinder cone. The other is the main tail. Both join up with each other shortly after the vista. At about 2210 meters, you have the choice of going straight through a cow gate or turning to the right (see images below) and following a fence line. There is a large tree covered with ancient vines marking the spot. Going straight will take you to an old lava flow and eventually to the southern end of La Meseta (The Plateau). Going right will take you to a very large and often active lava bed and the northern end of La Meseta. Total time to this point is about one hour. La Meseta is more or less a flat part of the northern edge of Cerro Chino (see images below). The cinder cone is clearly visible from this position. From here, you take a left, heading southeast, along the edge of the hill to the foot of the cone. The trail rises west to the top. The final push to the top of the cone is the steepest and most dangerous. Most of the climb is over very rugged terrain including fresh lava flows, scree, and deep ash. The final push takes about another hour to reach the lip of the cone. If you decide to climb the cone, be aware that you are taking a significant risk. Pacaya is extremely active and often throws large stones and other volcanic material from the cone. Also, there is the danger of breathing in poisonous gasses from the many fumaroles and the cone itself.
Plenty of Water, walking Stick, sun block, good shoes, and a snack or lunch. You may also want to bring a light jacket or vest and some rain gear.