Officially (at least what Google Maps says), Fenner Park is called "Carl G. Fenner Arboretum". We in the know just call it Fenner Park, because Arboretum is too many syllables for polite conversation. I've been going to Fenner since I was a kid, though the high water mark for visits was when I lived just off of Forest Road, which runs behind the park. Ah, that brings back fond memories of living in the duplex, like being awakened at 2:00 AM by a police officer asking if I had heard anything suspicious regarding the murder / attempted arson that happened a few doors down from me. Good times.
Fenner is 134 acres, a respectable size for being in the middle of town. The area was originally a farm, whose last owner, Scott Turner, sold the land in 1952 to the City of Lansing, the terms of the sale stipulating that the area remain in a "somewhat primitive" state. And thus it remains.
Near the front of the park is the nature center, filled with critters and exhibits, and holds nature-oriented events throughout the year. And in the "Be Kind to Animals" category, the pond behind the nature center has a man-made spring that keep the pond mosquito free and partially clear of ice in the winter in case Ranger Rick needs a drink during those long cold stretches.