On a budget, weigh it — Aventine Keyhole (Knights of Malta) isn't cheap for what it is.
Free
A genuinely magical 30-second trick: peer through an ordinary green door's keyhole and St Peter's dome sits perfectly framed by a hedge-lined path. It's free and charming, but it's a single photo op with often a short queue, so treat it as a delightful add-on to the Orange Garden next door.