Cruising into Mykonos in August with my wife. We are both in our 70's but adventurous and would love to know some off the beaten track ideas of must see activities and/or adventures, restaurants to try. We are limited in time to one day so realize time is a factor. Any thoughts would be greatly appreciated.

I agree: get to Delos to see the ruins if you can. Mykonos is so small there really aren't many "off the beaten track" places. The "heavily beaten track" is around the old harbour - Little Venice area, so get away from there and it will be quieter. You can walk up to Fabrika Square and take a bus to one of the beaches if you like, e.g. Agios Ioannis (St John) which featured in the Shirley Valentine film.