There is plenty to do in Yuscarán to keep you busy for a few days. Get oriented by heading to the main square in the center of town, admiring the whitewashed colonial vibe and exploring the Iglesia San Jose, which finished construction in 1768. Numerous colonial houses can be found in the streets surrounding the square, but none are as important as Casa Fortín (free admission; daily 8am-noon and 2-4pm), a national monument that dates back to 1850. The building was once home to the wealthy Fortín family, which was involved in various business operations in the region and briefly in politics. The building now serves as the de facto town museum. The caretaker will gladly show you around, though the mediocre displays don't need much explaining.
An interesting side excursion is the El Buen Gusto factory (free admission; Mon-Sat 7am-noon, Mon-Fri 1-4pm), where they distill Honduras's favorite spirit, Aguardiente, which is sometimes called guaro. Just walk up to the plant and ask at the door for a tour, and someone will walk you through while explaining the distillation process (in Spanish).
If you are going to stick around for a while, check in at the Fundación Yuscarán beside the town hall on the square. Here, you can get maps and information on trips to the nearby hot springs and petroglyphs near the town of Oropolí, or arrange guided tours to the cloud forests in the Monserrat Biological Reserve.
During the first weekend in June, Yuscarán's annual Mango Festival is the best time of the year to hang around. Anything quasi-mango is celebrated in mango bobbing, parades, dancing, and the election of a mango queen. The favorite event, though, is "Donkey Polo."