Nice variety of rail trails, state and county parks, nature preserves, a quarry and an arboretum. This is mostly flat walking. St. Joseph County offers many options.
A village, a historic canal, a deep valley and a rail trail provide options in Delphi, along the Wabash. The bridge is under reconstruction, but you can hike up to one end and you can hike beneath it in the valley.

Travelers have come to know and love the outdoor recreational facilities of France Park, with scenic trails, beautiful waterfall, clear swimming lake with picturesque cliffs, quiet fishing areas, and spacious camping facilities.


https://www.co.cass.in.us/departments/e-i/france-park/home
The Nickel Plate Trail runs from Kokomo to Rochester. There are a dozen trailheads along its 40 mile length. Although mostly flat, this is a surprisingly scenic trail where it crosses 3 major rivers and approaches Lake Manitou south of Rochester.

http://www.nickelplatetrail.org/
Visit Jasper-Pulaski any time, but come in the fourth quarter to see the truly amazing sandhill cranes.

https://www.in.gov/dnr/fish-and-wildlife/properties/jasper-pulaski-fwa/sandhill-cranes/
Deep River Park in Lake County follows the river, starting at an historic grist mill.

https://lakecountyparks.com/151/Deep-River-County-Park
Spicer Lake has trails and board walks for visiting the birds. This is a short hike, but quite memorable at the Michigan border.
http://www.sjcparks.org/591/Spicer-Lake
Plymouth, Indiana has a small trail system that connects the river and surrounding areas.

LaSalle FWA is part of the Grand Kankakee Marsh. Interesting trees, bushes and birds abound.

https://www.in.gov/dnr/fish-and-wildlife/properties/lasalle-fwa/
The prairie and stream trails are enjoyable. The Gabis arboretum resources and gardens are nice. But the highlight is the outdoor model train and landscaping.

Several interesting trails along the Tippecanoe River.
https://www.in.gov/dnr/state-parks/parks-lakes/tippecanoe-river-state-park/
Potato Creek is west of South Bend. The trails take advantage of a lake, historical and planted areas. The state is investing in this park for the future.
https://www.in.gov/dnr/state-parks/parks-lakes/potato-creek-state-park/
The Erie Trail is a straight 20 mile rail-trail segment of the American Discovery Trail, starting north of the Tippecanoe River SP and heading WNW to North Judson, IN.

https://www.prairietrailsclub.org/about
Surprising place for a nature park. This “savanna” landscape is just west of a heavily drained farm landscape.

A second St Joseph County Park. Pine trees, open spaces and a small stream highlight the trails.