Is it an illegal still for making gin, hidden in the countryside?

The clue is the cherry trees in the background. Hail showers destroy cherry crops and so the orchard is defended against hail stones by this building.

The tall chimney that looks like a megaphone is a megaphone. Inside the building, butane gas is exploded, and the shock wave is propagated out of the megaphone across the orchard. The shockwave pulverises the hailstones to dust, thus protecting the cherries.