Whuich runs from the Northwest edge of Chicago proper, snaking it's way north for 20 miles, ending at the Chicago Botani Garden in Glencoe. You also have the option of picking up another trail, the Green Bay Trail and going further.
The trail is paved, reasonably maintained and goes through some beautiful parks. I've seen deer at various times.
I've also used to trail for a portion of commuting to the office by bicycle occasionally.
This is one of the benefits of living around here.