The best replacement for hot tubs is jacuzzi.

The best alternatives to hot tubs are rated as following:
★★★★★  jacuzzi
★★★  spas
★★  saunas
★  cal spas
★  chlorine
★  220 volt hot tubs
★  pools
★  whirlpools
  portable spas
  backyard spas
  juzzi
  above ground hot tubs
  swimming pools
  beachcomber
  jacuzzis

Your alternative for hot tubs is not listed? Suggest!
Speaking about hot tubs, one probably shouldn't forget about gazebos.

Other search terms related to hot tubs and their ratings are:
★★★★★ gazebos
★★ decks
You have in mind a companion for hot tubs and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of hot tubs in all years. Click on graph for more.
hot tubs
jacuzzi
spas