Located in Glenns Ferry, Idaho, Three Island Crossing State Park is dedicated to the historic site of a ford on the Snake River of the Oregon Trail. To get there from Boise, travel on I-84 about 70 miles until you reach mile marker 121. Turn left on 1st Ave and take another left on Commercial Ave. Take a right on Madison and you will reach the park entrance in approximately 1 mile (There is a $5 fee per vehicle to enter the park if you don't have an Idaho State Parks Passport). The campgrounds themselves are visible from the entrance. 

Within the park there are 82 RV campsites with full hookups as well as 12 small cabins. All are reservable here (sites go quickly, especially around holidays). Within the park there are flush toilets and showers, and firewood is available for purchase at the site of the camp host. There is plenty of grass in the campground for kids to play as well as a horseshoe pit (bring your own horseshoes).

The park offers plenty of short hiking and running opportunities. Trails are not well marked, but they are all short and connect to each other, so it would be pretty difficult to get lost in the park. Wildlife is abundant, deer are frequent in the area, and bird watching opportunities are plentiful wherever you are in the park. For anglers, fishing access is available on the Snake river and a small pond called the Indian Hole Pond within the park that has at least 5 different species of fish (there are some gigantic carp in the pond and some trophy sized bass). River access is limited but kayaks and canoes (no motorized boat access) can reach the river in several places. You could kayak or canoe in Indian Hole Pond (ideal for anglers as there is limited access to the pond) but keep in mind the pond is not very large. 

As the park is dedicated to the Snake River crossing, there is a nice museum called the Oregon Trail History and Education Center (closed Sunday and Monday). The museum is very well done and provides a lot of great education opportunities about the region. The park overall has a wonderful, historic spirit that is felt throughout the park. 

Three Island Crossing is also within range of several hot springs (1000 springs, Miracle, Banbury) and Bruneau Dunes State Park (good fishing) if you feel like making a day trip to one of them.