What are some really fun things to do in El Salvador in the 'winter"?

I am going to El Salvador for summer break in 2 and a half days for one month.My mom works Monday through Friday and on Saturdays until 12, so we have a limited amount of places to go.We know we are definetely going horseback riding and to the beach, so that will take up like 2 days already.We only have 4 weekends so please make your list the top places to visit with a lot of people (about 10 in my family) Thanks!