My favorite is the Cascade Falls section of the Patapsco River Park. Above is the Bloedes Dam.
The Falls provides a nice place to take off your shoes and cool off during the hike up.
The Trail has some areas where you have some easy to manage stream crossings.
The swinging bridge near the entrance to the trail will connected you to the other side of the river and provide some additional hiking trails.
To preserve this beautiful area consider volunteering for the Patapsco Heritage Greenway effort.