How did Batman disguise the lever that opened the secret panel that he and Robin used to get into the Bat Cave?

I believe it was a head bust

In Batman Forever, the Batcave entrance was hidden behind a false locked door. Dick Grayson (Chris O'Donnel), watched Alfred walk into the locked door and flew in from upstairs and fell into the Batcave.

In the current Batman Movies, Bruce Wayne hits two specific keys on the grand piano which opens a bookcase revealing the elevator that brings him down to the Batcave. Since Wayne Manor in Batman Begins has been burned to the ground, we will have to see how Bruce sets up the new entrance to the Batcave.

It was a bust of William Shakespeare.

https://www.thegreenhead.com/2004/09/batman-shakespeare-bust-life-size.php