The Lucca Orto Botanico rest just inside the southern wall.
They seem bigger from the wall then when one is inside, like a reverse Tardis.
Access for wheelies is from the East end of Via del Giardino Botanico.
Just push the intercom and mention a sedia a rotelle and you and your friends can get in for free.
(no cheating if you are not a wheelie!)
My favourite spot is the fake hill just near the ticket office, up a steep spiral path.