The Loosdrechtse Plassen form a large nature reserve where water and water sports predominate. The lakes form the central part of a protection zone for birds, other animals and plants. The water-rich area was created by peat extraction, which caused water to gain more and more ground. The lakes consist of various waters that are separated from each other by dikes and islands. The Eerste to Vijfde Plas together form the Loosdrechtse Plassen by definition, whether the area also consists of other waters is up for discussion, because the border of the area is not clearly demarcated. National monument Kasteel Oudaen is the first sight you encounter. This former knight's manor was built around 1300. In the fifteenth century, the very old house was owned by a family that also owned the city castle of the same name in Utrecht. The original Gunterstein castle also dates from around 1300. The complex is named after its first owner. In 1511 the castle was demolished by the people of Utrecht who used the stones to restore the Bemuurde Weerd of Utrecht. In 1518 the second building was built, but it was set on fire by the French in 1673. In 1680 the new owner Magdalena Poulle had the country estate built as it still looks today. Fort Tienhoven was built between 1848 and 1850 to close off the Tienhovense Vaart. The fortress defended the inundation quay, a dam lock and a crow lock against hostile traffic over water. The fort is not accessible, but even from the outside the fort is an impressive building. The next beautiful building is that of Sypesteyn Castle. The building is said to have been built around 1288, but the oldest foundations of this complex date from around 1500. In 1589, the house was destroyed by skirmishes and shortly after the ruin was restored, fighting between French troops and soldiers of the stadtholder destroyed the castle again. Around 1900, the estate was purchased by Jonkheer Henri van Sypesteyn. He built a modest ancestral castle on the foundations of the ruins using materials from demolished historical buildings and churches. This castle is set up as a museum about the family, but the museum also houses collections of art and crafts. The castle garden is also beautiful: the park is over five hectares in size and a (castle) garden, a maze and an orchard have been created. These are separated by hedges, moats and ornamental fences from old country estates. When you arrive at Slot Zuylen, you will see that the castle is located in a small park. The one and a half hectares of land is enclosed by a serpentine wall. This wall is 120 metres long and is listed as a national monument. There are several national monuments on the site: the quay walls, a culvert, a bridge, the gatehouse, the corner tower, the coach house, the gardener's house, the castle farm, the wood storage and carriage shed, the playhouse, the iron fence and a vegetable garden are all of great cultural-historical value. The history of the first castle goes all the way back to the thirteenth century, when a keep was built here. The castle became increasingly larger and more extensive and in 1752 the castle was last extensively renovated. Today it houses a museum. You will then come across two forts: Fort De Gagel and Fort aan de Klop. Both are part of the New Dutch Waterline. Fort De Gagel was built between 1819 and 1821, with L-shaped earthen ramparts with gun emplacements, which were constructed behind excavated moats. From 1848 onwards the fort was significantly expanded. Among other things, a bombproof guardhouse of 256 m2 was built. A moat was also constructed around this guardhouse and this building was also equipped with (heavy) artillery. Forty years later, the fort was reinforced again, with the moat around the guardhouse being filled in and the guardhouse being drastically renovated on the inside. The condition of the guardhouse now is the same as after the renovation in 1880. Fort aan de Klop was also built in 1819. This fort is located in a strategic location and defended Utrecht. This fort is used for recreational purposes: you can camp there, have a cup of tea in the teahouse or spend the night in an inn. Between the restored historical warehouses and the old guardhouse, you will feel like you are back in time! The last sight during your tour is Slot Zuylen. The castle is located in a beautiful park, on a plot of land of one and a half hectares that is enclosed by a serpentine wall. This wall is 120 meters long and is on the list of national monuments. There are several national monuments on the site: the quay walls, a culvert, a bridge, the gatehouse, the corner tower, the coach house, the gardener's house, the castle farm, the wood storage and carriage shed, the playhouse, the iron fence and a vegetable garden are all of great cultural-historical value. The history of the first castle goes all the way back to the thirteenth century, when a keep was built here. The castle became increasingly larger and more extensive and in 1752 the castle was last extensively renovated. Today it houses a museum.