Any idea what this is - please?

[wilfandrowlf]

I came across this whilst out walking the dog on Saturday. It appeared to be fixed to the ground in the woodland, just to one side of the footpath.
It’s about 4” square and the silver disc on the top looks like it’s made of aluminium.
The silver disc felt like it was spring loaded and I thought maybe it would release a secret door in the hillside, subsequently leading to an underground bunker, filled with exotic and rare classic cars, all looked after by a group of scantily clad ladies with maybe a fully stocked bar and humidor.

Sadly it didn’t.

The dog sniffed it briefly then completely lost interest and ran off in to the woods!
I thought to myself that someone on PH is bound to know…….so over to you guys.
Many thanks

[Charlie1986]

Do you have any military units near by?

Looks like a trigger plate set up for instructing IED's

[andym1603]

See two of these where I walk the dog near here. They are in scrub land and are flush with the land but do not have the silver disc on top. Always thought the could be reference points. I await a proper answer.

[Mr GrimNasty]

http://www.surveyingequipment.com/product/500mm-sp...

[wilfandrowlf]

Many thanks, it all makes sense now.
No idea what they could be surveying, its all National Trust owned woodland.

I liked my idea of the underground bunker more but hey ho!

[droopsnoot]

It's a bit obvious to be a door-release for a secret underground bunker, though - you need to start walking through the woods twisting alternate branches in opposite directions, sticking your hand down rabbit-holes, that kind of thing, or you'll never find it. They don't make them that easy to find, you know.

[wack]

Move it 10ft then when they build the tunnel leading to the secret bunker they'll miss

[perdu]

They disable them whilst they are awaiting restocking of the bar

Try again next Friday, they deliver Thursdays