What are some fun, family activities i can do with my 3 kids over the summer?

i have 3 kids, 4, 2, and 10 months, since its summer i was hoping to take them on some fun day trips. what are some fun activities we could do? i was thinking once and a while i'd get a baby sitter for the youngest, and only take the 2 and 4 year old, or sometimes just the 4 year old, so that they could do some more fun things. what do you think?