Rheinfels Castle construction was started in 1245 by Count Diether V of Katzenelnbogen. After expansions, it was the largest fortress in the Middle Rhein Valley between Koblenz and Mainz. It was slighted by French Revolutionary Army troops in 1797.
The main entrance to the castle complex is a tall square clock or gate tower (~1300 AD) opposite the hotel. A connecting path joins the clock tower to the remains of the living quarters of the Earls of Hessen-Darmstadt (the so-called Darmstadt Building). The Darmstadt building was designed in Tudor style with pointed gables. The connecting path was the site of the former moat of the main castle buildings; part of which is now the large cellar or basement. This large cellar was arched over in 1587-89 in two visible phases. It is the largest self-supporting vaulted cellar in Europe and has a length of 24 metres, a width and height of approximately 16 metres and can accommodate up to 400 people.
The walls are up to 4 metres thick. Previously a 200,000 litres wine barrel was constructed for storage. The cellar was renovated in 1997 and restored to its original condition and now serves as a meeting place for concerts, theater performances, and other shows.
The castle museum is located in the former castle chapel which is the only finished room of the original castle. It is accessed through an internal gate and up the path. The museum contains a model reconstruction of the castle before its destruction giving one a sense of how big the castle used to be. The medieval castle courtyard is found beyond the castle museum building (slightly uphill). This was the center of the medieval castle which contained a bakery, pharmacy, garden, brewery, well, and livestock—which would have allowed it to withstand an extended siege. Remnants of the original 13th-century plaster which was painted white can still be found on some walls.
While much of the castle is a ruin, some of the outer buildings are now a hotel and restaurant.
References:Herceg Novi was founded (on a former small fishing village, existing since Roman Empire times) as a fortress in 1382 by first Bosnian King Stjepan Tvrtko I and was called Sveti Stefan or Castelnuovo. The Turks conquered Herceg Novi in 1482, and ruled for 200 years, until 1687. However, there was a short pause between 1538 and 1539 when it was held by the Spaniards before they were defeated in the Siege of Castelnuovo. Turkey ruled again until 1687, from then until 1797, the town was ruled by the Venetian Republic.
The Herceg Novi old town is amazing. It is on a fairly steep hill that leads all the way down to the sea. Wandering through the small stairways to the various plazas and fortresses is a many hour adventure.