Splash Lagoon is Erie's big indoor water park, built around slides, wave pools, lazy rivers, and warm humid air that feels very welcome in a Lake Erie winter. It is not a cultural sight, but for families it can be the difference between a short stopover and a full extra day in town.
The park sits near the interstate hotel strip rather than the waterfront, so plan it as a dedicated activity rather than something you wander into from downtown. Book ahead during school breaks and bad-weather weekends, when the place fills with regional visitors.