How did Alice get into the garden?

Alice drank the liquid she found on the table, which was labeled "DRINK ME".

However, this bottle was NOT marked `poison,’ so Alice ventured to taste it, and finding it very nice, (it had, in fact, a sort of mixed flavour of cherry-tart, custard, pine-apple, roast turkey, toffee, and hot buttered toast,) she very soon finished it off.

`What a curious feeling!’ said Alice; `I must be shutting up like a telescope.’

And so it was indeed: she was now only ten inches high, and her face brightened up at the thought that she was now the right size for going though the little door into that lovely garden.