Bubi352,
Some of the very early A320's had a lift up hatch in the aisle for access to the avionic bay below. It was situated under the carpet just aft of the forward galley. Didn't really use it a lot because once open, it impaired boarding. On a quick turnround it was much easier to get the ladder out and enter the bay from outside. The hatch was gradually done away with as it became obvious it was more bother than it was worth.