The Marvelous Bridges (Bulgarian: Чудни[те] мостове, Chudni[te] mostove) is a rock formation in the Rhodope Mountains in southern Bulgaria. It is located in the Karst valley of the Erkyupryia River in the Western Rhodopes at 1,450 metres above sea level, at the foot of Persenk Peak.
The "bridges" were formed by the erosive activity of the once high-water river. It transformed the marble clefts into a deep water cave, the ceiling of which whittled up through time and collapsed, allegedly during an earthquake. Geologists suppose that the water carried the debris away.
As a result, the two remaining bridge-shaped boulders remained. The large one (situated upstream) is 15 metres at its widest and 96 metres long, and shaped by three vault arches, the largest of which is 45 metres high and 40 metres wide. The Erkyupriya River flows under the middle-sized arch. The large Wonderful Bridge is passable under the vaults where birds nest in the marble clefts. The smaller bridge is located 200 metres downstream. It is unpassable, 60 metres in length, with a total height of 50 metres, 30 metres at the highest place of the arch. A third, very little and hardly reachable bridge-like formation follows, constituting the entrance of a pothole cave where the river waters disappear underground, and show back up after 3 km.
The adjacent area is timbered by century-old conifers, mainly spruces. Near the rock formation many Karst caves have been discovered, but most of them are not electrified and safeguarded, thus unsuitable for touristic visits. However, both bridges are safeguarded and can be walked over. Two tourist huts are located nearby. The place can be reached by an asphalt road and is about 30 km from the closest town of Chepelare.
The Wonderful Bridges is included among the 100 National Touristic Places of the Bulgarian Touristic Union, under number 85.