Where to take disabled father for scenic trip, North America

Hi all!
I would appreciate any advice on where to take my nearly 70 year old father for a short (week ish) trip. I’ve been abroad for a few years and want to make a great trip for him while visiting home.

He is really interested in nature and loves the water (lakes or sea is fine). My brother and I really want to take him somewhere within a 6 hour flight max from Chicago.
Also willing to drive more than that as none of us mind the drive and could extend the trip a few days for this if needed. My dad is pretty easy going about what to see, but in general appreciates the national parks or wildlife or just nature and water in general. The issue is that he is old, and has health issues that really impact his breathing. This means no really high altitudes for him.

Does anyone have any suggestions on potential places to bring him? Maybe somewhere that does something like a guided tour through a car/transport sort of thing. My brother mentioned something like the tours that are for sight seeing for bears or maybe something along those lines.

Edit to add some of his other interests: boating (huge fan of boats in general), animals, doesn’t like to drink, not too much of a foodie. He’s a very very curious person and really always interested and hears people when they are talking about a passion or common interest. Thinking a private tour of some sort might be good

Edit 2: some great replies here!! Train would be also great option (: he loves sights from the train

Really appreciate any insight. My dad is getting older, and I’ve been away for some time and really want to make a great holiday for him while I can. Many thanks