You can take bus #249 from Sonsonate towards Berlin and Alegria. It will take you about half an hour to arrive at the Parque Central.
Bus 348 from Usulutan comes to Alegria through Santiago de Maria. But be careful as we arrived at 4:45 to catch a bus from Usulutan to Alegria and the last bus had left already, or so we were told by the locals and we didn't want to chance getting stuck in Usulutan. We were able to taxi for US$20 and it took just under an hour to get into town.
Laguna de Alegría (also known as the Emerald of Central America). The laguna is inside the crater of the now dormant volcano Tecapa. The laguna grows a brilliant green especially in bright sunlight, which is caused by the sulfur and other minerals found in the craters volcanic clay. It is a favorite spot among El Salvadorans and its common to see locals trekking out hunks of the clay which they use for medicinal purposes. There are several picnic tables and large rocks to congregate around. The laguna itself is only deep in the very center although most El Salvadorans will not swim in the laguna. There is a myth that a mermaid lives in the laguna which drowns handsome young men. The cobblestone path is roughly 1.5 miles long and is a moderate hike through coffee plantations. The road will end at the entrance to the laguna and a small tienda is just to the left of the entrance. Admission is 25 cents for the day. edit
Casa de Huéspedes La Palma, 1a avenida Norte (near calle Alberto Masferrer, in front of the Parque Central), ☎ 2628 1012. Eclectic items in the owners home/hostel which are fun to look at, and the owners are very nice people. A room with two single beds cost $10US a night per person. Hot showers, wifi, and a great location. edit
Cabañas La Estancia de Daniel. Family atmosphere.From $10. edit
Hostal & Café Entre Piedras, (northeast corner of Parque Central), ☎ 2313-2812 (email@example.com), . Opened in 2009. Hot water, cable TV, Wi-Fi. Good restaurant. Very nice patio to sit, relax and have meal. www.hostalentrepiedras.com From $16. edit