The Grate in the Building wall

At the bottom edge of the grate there was a handle so it was definitely meant to be used by someone with hands. I reached out tentatively and grabbed ahold of the handle and pulled lightly to my relief the grate came up soundlessly, and I crawled inside lowering the grate carefully behind me. Turning I found myself inside a very dark but clean ventilation tunnel. Realizing I was still clutching my flashlight from earlier I crawled inside the vent and flicked it on,