Illinois does not have any national parks, but it does have several national historic sites, trails, and recreation areas. One popular destination is the Lincoln Home National Historic Site in Springfield, which preserves the only home Abraham Lincoln ever owned. Visitors can take a guided tour of the restored home and learn about Lincoln's life and legacy.

Another interesting site is the Pullman National Monument in Chicago, which preserves the historic Pullman neighborhood, a planned community built for workers of the Pullman Palace Car Company in the late 19th century. Visitors can explore the historic architecture, learn about the labor movement and civil rights struggles that took place there, and take a guided tour of the factory site.

Other national sites include the Lewis and Clark National Historic Trail, which traces the path taken by the famous explorers through Illinois and other states, and the Trail of Tears National Historic Trail, which commemorates the forced removal of Native American tribes from their ancestral lands in the 1830s.

The best time to visit these sites varies depending on the weather and the specific activities available. Spring and fall are generally pleasant times to visit, with mild temperatures and fewer crowds. Summers can be hot and humid, but offer more opportunities for outdoor recreation. Winter can be cold and snowy, but some sites offer special events and activities during the holiday season.

Overall, Illinois offers a wealth of national historic sites to explore, each with its own unique history and attractions. Whether you're interested in learning about Abraham Lincoln, the labor movement, or Native American history, there's something for everyone in the state's national sites.