The best replacement for diving is snorkeling.

The best alternatives to diving are rated as following:
★★★★★  snorkeling
★★★★  gymnastics
★★★  skydiving
★★★  bungee jumping
★★★  swimming
★★  scuba diving
★★  padi
★  free diving
  sky diving
  cliff jumping
  deep sea diving
  figure skating
  navy diving
  pacific diving
  scuba

Your alternative for diving is not listed? Suggest!
Speaking about diving, one probably shouldn't forget about gopro.

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



Google Trends

Scale is based on the average worldwide traffic of diving in all years. Click on graph for more.
diving
snorkeling
gymnastics