If you are in the central Illinois area or planning on visiting, I can't reccomend a more unique experience than Allerton Park. It's just next to (all but inside of) Monticello, Illinois. It is especially good for anyone who enjoys nature, sculpture, history, and architecture. It's been deemed a national landmark and was donated to the University of Illinois in 1946 by Robert Allerton. Allerton Park is open for free to the public. They do accept donations and certain parts of the mansion are generally off limits due to events. You can even reserve part of the mansion for your own events such as a wedding. That will cost you some cash, but for a lot of people its well worth it.
This is one of those places that defies definition or at least a simple one. If you like intricate flower gardens, this is a good place to visit. If you like wildlife, you'll like it here. Awesome statues with an Eastern influence can be seen throughout parts of the park. There's even a "Sun Singer" statue with an interesting history and in some ways remeniscent of the statue of liberty. There are paths you can walk down to access most parts of the park. Kind of off one of the paths is the pioneers cemetary, complete with tombstones dating all the way back to the 1800s. Besides the mansion which you'll see upon arriving in the guest parking lot, there are some awesome architectural places. One of the favorites of most people is "the Sunken Garden". The cool thing about the sunken garden is that you can have one person at the top of a stair case on one end and another at the top of the stairs on the other end and hear eachother whisper. Just try to get the area to yourselves for a moment to try it out. Near most of the statues and gardens, you will find message boards giving information and history on the exhibit.
Allerton also has a 4H program and cabins set up for school field trips. In fact, the first time I personally went there was when I was in sixth grade and it was our big trip for the year. Our trip consisted of three days of exploring the park, observing nature, a bonfire, a square dance, and all kinds of memories. It was enough to make me and many of my friends want to keep coming back well into our adult years and to bring our families. My fiance has referred to Allerton as her favorite place in the world on several occasions.
A few other suggestions if you decide to give this place a try are "The Dying Sentaur" statue and "The Musicians" statues. There is also a section just before the visitors parking lot where the "Fu Dogs" are located. These statues are of Eastern influence and very popular among many who visit. There is even a cool tower with a spiral stair case which you can climb up. It overlooks the Fu Dogs and gives you a great view. The picture included with this article gives just a brief glimpse of one of the areas of the park. You can see some of the tall trees in the background and some of the musicians statues in the foreground. It can take quite a while to walk through the whole park, but it's a good day trip. Just remember to bring something to drink with you as you walk. There are usually pop machines near the parking lot and bathrooms near one of the flower gardens. Another piece of advice; Bring a camera. You'll be glad you did.