Periscope

[Outdoorsman2]

I want build a long-ish one - to see what is happening in a local disused stone quarry. There is tall mound of earth blocking my view. Any ideas please on how to make a periscope from common or garden materials? I think there is an animal sanctuary being built and, as I'm a keen naturalist, I want to get involved. But I want to make sure it is a legitimate enterprise.
Thanks.

[Khandro]