The backyard of my new house is like a giant Myst puzzle. So far, I've found two things that have both timers and switches involved, one of which the previous owner told me did not work so she apparently never figured out (cabana lights - she'd strung Christmas lights in the cabana because she could not get the built-in lights to work).

The "fun" part of the timer/switch combo is that they are generally not on the same panel or obviously related, so to figure this out you have to try flipping switches that do not appear to do anything, then either leave it that way and check back regularly to see if anything changed, or find something that might be a timer and play with it while the switch is on.

Next, I aspire to figure out how to turn on the water in the cabana. I suspect it's one of the forest of knobs under the sink in the utility room in the main house.