You must first take a bus to Herida. Buses leave from San Jose to Herida every 15 minutes 6AM to 10PM from Calle 10 & 12 and Avenida 2.
From Herida, you must take a bus to Paso (passing through San Jose de Montana). Llano and then Sacramento. Buses currently leave at 6:30AM, 11AM, and 4PM. Ask the driver to let you off at the track to Volcan Barva. From there it's 3 kms to the actual trailhead and national park entrance station. Unless you either are lucky and get a ride or have your own vehicle, you will have to walk this distance.
From the entrance station, follow the sometimes muddy trail to Lago Barva which is reached after 2 kms. On the lower slopes, the trail passes through cattle pastures, but soon these are left behind and you enter the rainforest which very thick in this area. Keep your eyes open for wildlife and search the trees for the beautiful quetzal (bird) as this area is said to be one of the best places in the country to see one.
Just past Lago Barva, keep an eye out for a faded trail up to the crater rim of Volcan Barva. The trail is steep in places and can be hard to follow. The summit of Barva is 4kms from the trailhead. Expect to take four to five hours round trip from Sacremento in good weather.
Blue-Crowned Motmot, Volcan Barva.
A good pair of boots, camera, rain gear, and a jacket.