Marvelous Bridges, Natural marble arch in the Western Rhodopes, Bulgaria

The Marvelous Bridges (Bulgarian: Chudnite mostove) are two natural marble arches in the karst valley of the Erkyupriya River, Western Rhodopes, at 1,450 m. The larger, upstream bridge is 96 m long and 15 m at its widest, with three vaulted arches; the largest arch is 45 m high and 40 m wide, and the river flows under the middle arch. The smaller bridge, 200 m downstream, is 60 m long and 50 m high overall, with a 30 m arch, and is not passable for visitors.

The arches formed when the Erkyupriya River, once larger than today, eroded cracks in the marble into a deep cave. Its ceiling thinned and collapsed, possibly during an earthquake, and geologists believe the water carried the debris away, leaving the two marble bridges.

The name Chudnite mostove means "wonderful bridges" in Bulgarian; the site is also known as Erkupriya, from the Greek for "wide gate". A local custom has visitors write their names in charcoal on the wall under the large bridge, despite a fine of 500 to 5000 leva. The bridges are number 85 among Bulgaria's 100 National Tourist Sites, with a stamp for collectors.

The site lies a few kilometres from Zabardo; the 8 km access road after the turn-off is in poor condition, with difficult passing and undermined sections, and is risky for low-clearance cars. Both bridges are secured and adapted for tourists, and crossing is allowed both over and under them. Two huts nearby, Chudnite Mostove and Skalnite Mostove, are managed by the Studenets tourist society of Chepelare.

The marble here is what remains of a cave roof: the Erkyupriya once flowed through a deep water cave, whose ceiling thinned and collapsed, and the river carried the debris away. The third, smallest opening downstream is a ponor where the water sinks underground and resurfaces 3 km away.