The birds will fly a couple of miles to water if necessary, but they prefer to nest within a half mile of a lake or other water. I know people in my small town of Fairfield, Iowa, who attracted Purple Martins to their martin house even though there doesn't seem to be any water around. But if you look on a map you'll see that the town reservoir less than a mile away. Both covet Purple Martin houses and will take them over if the landlords let them. In order to do this task, you need a method of raising and lowering the nests for your inspection.
Most systems utilize telescoping poles or a winch and pulley system.
The winch and pulley system is easier to use, because the martin houses can be heavy when they're full of nests and eggs or babies. Don't be intimidated by the task of examining the nests. The Purple Martins won't mind in the least. Remember, they LIKE people. And they will have greater nesting success if you do your job.