It was a question on the Aikido Journal website as part of a sales promotion of posters of O'Sensei. Very nice posters that I am still considering, but the question is such a good one it deserves an answer.
When I am the first one there and I unlock the door and enter, it is quiet, the lights are out, the image of O'Sensei and Suenaka Sensei on the shomen dominates the room. The overall experience draws me in and it is a sense of the holiness of the place that always catches me.
Every class is a gift.