The Cleveland Zoo is a gem! The layout of the zoo itself makes it a great active way to spend time with friends and family. However, if you have young kids or older persons with you who cant walk as far, there is a shuttle that'll take you to the farther areas. Tickets are relatively cheap, but I recommend getting season passes because they're definitley worth it. I believe Mondays are free.
The rainforest is not a part that you want to skip! It's a beautiful indoor experience with some amazing plants and creatures. I love that there is an aquarium here as well. Definitley a great place to spend the day on a date or with the family.
Additionally, parking is free and they let you bring food in so PACK A LUNCH! And don't forget a water bottle!