ido style folder navigation

ido allows you to use C-j to view the current directory. If you press RET on a directory, completion continues from that directly.

This is easy to configure with ivy:

;; Use C-j for immediate termination with the current value, and RET
;; for continuing completion for that directory. This is the ido
;; behaviour.
(define-key ivy-minibuffer-map (kbd "C-j") #'ivy-immediate-done)
(define-key ivy-minibuffer-map (kbd "RET") #'ivy-alt-done)

If you want to use the default ivy keybindings, C-j will continue completion on a directory, and C-M-j will view the current directory.