i've been there. it's a pretty cool place. free to get in. here's a link for you. http://www.in.gov/dnr/outdoor/4226.htm
it's old coal mine property, so it's fairly rocky.
there's pretty much something for everyone there. rocks, mud, tight technical trails, etc. it's a fun place. here are some pics from when we went....
me....
i thought this hole was gonna get me. had to do the ol' "see saw on the steering wheel" and mash the skinny pedal, but i made it through.
my Dad in his stock TJ coming down one of the bigger hills in the open area. the pic doesn't really do it justice.
on the 16th, this is going on.... http://www.naxja.org/forum/showthread.php?t=1016327 which i'll probably be going to. so, you may not get many takers to go to interlake. if i was going to the m&g i'd be down for going. it is cool place. be sure to take pics and video if you go!