Sybil's Cave is a small stone arch tucked into the waterfront cliff at the north end of Frank Sinatra Drive — the rebuilt entrance of a 19th-century spring that once made Hoboken a summer resort for New Yorkers escaping Manhattan's heat and water-borne disease. Closed and largely forgotten through the 20th century, the cave was rebuilt in 2008 with a new iron gate and an interpretive plaque.
The cave itself is gated and you cannot enter, but the spring is back to flowing. It is the kind of small, strange landmark that says more about Hoboken than the bars and boutiques nearby. Pair it with a walk along the cliffside above the river.