If this land has native stone, it must be made from that, otherwise it will have no "mana".
If you have no native stone, but there is stone or concrete rubble from structures past, this will suffice.
Structures, walls & inlaid stepping stones seem to be waning in popularity, but I think they add a little mystery or a touch of something past. All my raised beds are made from stacked stone & I like the "ruin" look they have plus they are fun to make. Be carfeul, once you start stacking stone you wont want to stop :)

It's been done before. Google Stonehenge, Goldendale, Wa.
It's in the middle of no where. Made from concrete. Read the reviews and take a look at the pictures.
I have visited it several times.
Mike

I'm pro real stone too. That's what gives it character. What about a different shape- like a StoneDeca?

If you can get the stone, and can afford it, go with stone. If you want something reminiscent of Disney, use concrete. You could always do a smaller scale than Stonehenge to keep the effort and cost down. There are a lot of different, unique, ancient stone circles in the UK. Pick one you can manage, or design your own.

how fun!

Faux stone for sure. I recommend casting the pieces in white concrete over metal lathe. White allows brighter color when a coloring agent is used. Color the concrete and press wrinkled foil into the surface as it sets up. I've seen amazingly realistic results using this technique. I would experiment with the color to mimic the look of the natural stone used in the real stonehenge.

Wooden blocks with slots and tabs could be attached to the lathe at the tops of the pillars and to both ends of the bridge pieces and left un-concreted. That way you could do a test fit of the entire mock-up, and make any adjustments to the alignment, before commiting the pieces to concrete.

The key to this project is that it acheives the same alignment with the sun during the summer and winter solstices as Stone Henge. Or, if you want a unique interpretation of the original, you could make the components in the shape of giant bones and call it "Bone-Henge". Just a thought.