Are you asking on how to hide it? If so, can you put flower beds around it and plant taller plants that will hide it?
Marjie P, I think if you post a picture of the well and/or plastic rock you can get a lot of help & opinions.
You could also paint it to camouflage it to blend into the grass, fence, mulch or whatever you might have behind it.
Build a wishing well over it.
And how big is big?
I don't understand...how did getting a new well create a plastic rock? Is this a cover for the pump? A well usually means rural living or a place containing property. Like it or not, having been raised in the country, a pump house is you best bet. If you do not want to get creative and put in a pump/storage house, think of fencing off the pump and creating a relaxing place....pergola with patio with relaxing chairs, gazebo, patio with fire pit and grill, etc. You would then never know the pump is there.
Jeanette S, some people buy the big plastic rock to cover the well. Since I have 2 wells I can tell you that it is easy to cover my well and my rental home well with bushes & plants. Being in an HOA we are required to do so & it looks nicer than plastic. Both of my houses have very large lawn areas & city water was exorbitant.