Now I'm hearing about saunas and cold plunges. 

If I had to choose, I'd go dishwasher and provide portable induction cooktops.

Or for a hot tub/sauna? 

Sauna, hot tub and/or plunge, outdoor shower, massage table, pull up bar and some weights or TRX.

Targets smaller properties ($300K–$450K 10% down remaining for new furniture, sauna, fence, firepit, backyard ammenties, etc.) with room for value-add improvements.6.

.-- Furnish it with quality, design-forward furniture (like @Collin Hays said)-- Add one or two killer amenities (hot tub or sauna always do well in Denver, Colorado Springs and the mountains here.)-- Pay a high-end real-estate photographer to shoot a mix of photos from full-daylight and sunset.Good luck!!

Quote from @Theresa Harris: He should have a portable AC unit in his bedroom, but if they (the tenant) are causing damages/excessive wear and tear, do not renew their lease. 

We did provide a portable AC unit which is working.

It’s happened once in 7 years and I was only 3 hours away, but chose to ask a friend to help me out instead of leaving a family vacation to drop off a portable AC to a tenant whose AC went out on the weekend in the hot Florida summer.  

They (and Costco) have oft good deals on Sauna's / Cold Plunges - all the rage here.