You cannot see over the stone wall surrounding this yard, no... but the gate is still open, and there is no guard currently posted.
Like any hedge or bush, any determined child can worm their way through, usually by going under first, lifting up little prickly branches and sliding along the ground until there's more room. Once you get inside a hedge or bush, lack of sunight makes for less growth, and thus greater ease of movement. When it comes to hedges alongside buildings, the back side of the hedge is ALWAYS thinner than the front. Again, for sunlight reasons. You can make it through.
Along the wall of the house, you can see now that there are basement window wells which the hedges cover over. You might be able to open them.
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RAPRAPRAPRAP echoes the door as the sound of your knocking fills the hallway beyond.
It takes a few moments, but eventually, a stern looking man dressed quite well (in white and green) comes to the door and opens it. "Yes? Hello? Who are you?"