The foundation of the building doesn't look very "heavy duty" to me, nor do two small-ish bolts on a virtually unmarked plinth.
So that suggests either a compressor, or a small fan, or a generator set. The "window" appears to have had a some sort of (louvred?) cover which might suggest an air intake or exhaust. There's also a niche or entry through the brickwork to the right of the plinth in the internal view.