Recommendation for an overnight side trip between Kyoto and Osaka? & more..

Hi everyone! Firstly thank you to everyone who has ever contributed to this subreddit...this is my second trip to Japan in the past year and even when I'm not planning a trip I'm regularly browsing and lurking 'cause I love reading all of your recommendations and anecdotes.

That being said...I have done a bit of research (searching & using the sidebar, please don't crucify me) but am hoping to get some more opinions on my upcoming trip.

My itinerary right now is:

6/30 - Osaka (arrive KIX ~3pm)

7/1 - Osaka

7/2 - Osaka (check out of hotel)

???

7/3 - Kyoto (check into hostel)

7/4 - Kyoto

7/5 - Kyoto (depart KIX ~4pm)

I'm looking to go somewhere early on 7/2 and spend the whole day & night there before settling into Kyoto on 7/3. I know this is a pretty short trip and some might advise against trying to fit in too much, but I'd really like to fit in just 1 more unique experience in my trip. Something like a whole day at Koyasan or Nara, or even an overlooked city north.

I'm a 25 year old guy from the U.S. and travelling solo; my interests truly vary...so I'm hesitant to list anything I'm specifically looking for. I love anything off the beaten path and really try to avoid anything too touristy, but if it's something that has to be tried then I have to be a tourist. I think it's very cliche but, I'm very much into the "Bourdain" style of trips.

Anyway if anyone who reads this feels they have some good advice or any recommendations, I would truly appreciate it.

Thanks!

edit: maybe I should add I spent 2 days in Kyoto last October; but have never been to Osaka.