Right side of the road
If you are staying in El Salvador for less than 90 days, there is no tourist visa requirement for US Citizens. El Salvador is a part of the CA-4 agreement. The CA-4 agreement includes El Salvador, Guatemala, Honduras, and Nicaragua. It allows for free movement across these countries' borders.
Entry and Departure Taxes
There are no entry and departure taxes for El Salvador. Also, based on my experience, you will not receive a passport stamp when entering and exiting El Salvador.
To get to El Salvador, I took the King Quality (aka Platinum) bus from San Pedro Sula to San Salvador. The cost was 1100 Lempiras (~$47 USD). The bus station was located in an old shopping mall that was turned into a bus terminal. Personally, I did not think that it was obvious that the building was a bus station. There were colectivo buses outside but no sign of large international charter buses. You must go inside to find the charter bus company stores. The King Quality/ Platinum bus experience was excellent. The seats are large and comfortable. They recline to about 160° and the headrest is exactly like a pillow. They also serve you a number of meals, depending on the length of your journey, as well as coffee/ tea and a snack. The bus can get kind of cold, but they provide you with a blanket and a pillow, so it's not too bad. The bus dropped me off right in front of my hostel in San Benito, which is a safer part of town. The bus station is on Bulevar del Hipodromo.
To depart El Salvador, I used the King Quality/ Platinum bus again. The experience was excellent again. I took the bus to Nicaragua and you have to pass back through Honduras, which requires you to pay the $3USD Honduran entry tax. The only issue I had with the bus is that it arrives in Managua around 2:00am, which made me a little nervous. Unfortunately, this cannot be avoided. Otherwise, the experience was excellent.
While in El Salvador, I stayed at La Zona Hostel. The hostel was nice. It had a very nice common area with a hammock and a few tables and chairs. There was also a bar where cheap local beer was sold. I stayed in a eight bed mixed dorm and they were nice. The rooms were equipped with lockers for your important belongings. The lockers were not big enough for your whole backpack or suitcase. The bathroom was attached to the room and was fairly clean. Laundry service is available at the hostel, but was a bit expensive. The only complaint I have is the lack of organization at the hostel. On the day of my departure, the hostel manager claimed I had not paid them, when I had, so make sure you maintain evidence you paid them. All in all, it was a good experience.
While in El Salvador, I volunteered with FUSALMO. FUSALMO offers an alternative to the problems of children and youth, mainly of lower economic status and in conditions of risk, through the promotion of sports, arts, technology, entrepreneurship, etc. The organization complements these aspects with a training in culture of peace, values, human rights, and respect for the environment.
As a volunteer, I spent most of my time presenting to the students of FUSALMO about peace culture, my mission through Peace Stamps, and the importance of education. San Salvador has a large gang presence, so it was comforting knowing that I may have influenced children to forego the gang lifestyle and continue to pursue their education.