Rehabilitate a Prehistoric Pool

[prehistoric]

I was hoping I could get some guidance from the members. We own a summer cabin that has a prehistoric pool from the early 60s. The pool is solidly built (pure concrete all around about 15k Gallons). The pool has not been used in 20 years and when it was used, it was never used more than a couple of months a year. The pool never had any filter equipment or heater or anything that you may expect an in ground pool to have. We would like to rehabilitate the pool to use during the time we are at the cabin (a couple of months a year). Amazingly the pool still holds water well (we have used it as a rain deposit for watering the property). I was hoping to find efficient, low maintenances and hopefully not to expensive equipment for filtering and heating the water (ideally the same system, but can be two different components) that then can be stored after the season ends and reused the next year. Ideally the system would connect easily to PVC external piping that we would preinstall on the outside of the pool (esthetics are not essential). The system would have to be located on top of the pool (about 2 to 4 feet above the water line). We were thinking that perhaps above the ground systems would work better than in-ground equipment. Any guidance would be appreciated.

Thank you very much!