If you’re planning to spend a bit of time in the area outside of the wedding, there are several places to enjoy nature, art, and culture. However, most of it will require some travel.
There’s an extensive system of trails near Lake Charleston, and Fox Ridge State Park has a pleasant little river running through it. It’s May, so wildflowers should be in bloom. Allerton Park & Retreat Center (where the wedding ceremony will be held, weather permitting) is also a world-renowned formal garden full of art deco and East Asian statuary.
There are art museums at Eastern Illinois University and the University of Illinois, and there are a number of fun restaurants in both Champaign and Effingham. However, it’s graduation weekend at UIUC, so Champaign will likely be crowded, and some venues may be closed.
If history is more your thing, the state capital, Springfield, is about 1.5 hours away and has a large number of museums and historical sites primarily dedicated to Abraham Lincoln, as well as Lincoln’s Tomb, which is a somber marble masterpiece.