What is the best Halloween activity in Cincinnati for adults?

There are a lot of great haunted houses that are more suitable for adults than kids. You might want to check out both the Dent Haunted Schoolhouse and the USS Nightmare riverboat.

It might not be for everyone, but Cincinanti's annual Zombie walk is a ton of fun. It's on October 20 this year. They start at the Freedom Center, parade through Downtown Cincinnati and end up on Fountain Square. Bars sponsor special nights and some have parties: http://www.cincinnatizombiewalk.com/

Northern Kentucky also has a Zombie Walk the week before on 10-13-2012. http://nkyzombiewalk.com/