Altenberg Abbey / Altenberger Dom
Altenberg Abbey was founded in 1133 as a "daughter" of Morimond Abbey and, as Cistercian monks do need running water nearby, moved to this place near the Dhuenn river 20 years later. The monastery flourished and so a number of daughter houses in the "Wild East" were settled from here: Wagrowiec 1143, Zinna Abbey 1171, Haina 1188, Jueterborg 1282....
In 1259 the erection of the Gothic basilica style church named "Altenberger Dom" (or "Bergischer Dom") started, replacing a Romanesque structure. In 1379 the church got consecrated.
Having entered the church - facing east. The nave is about 80 meters long - and flooded with light.
The monastery existed until 1803, when it was dissolved during the secularisation. The inventary was auctioned. The buildings were sold to a merchant from Cologne. He leased them to two entrepreneurs, who established a chemical plant inside the church.
The explosion of this plant destroyed large parts of the structure in 1815. The complex fell into ruins, before from 1847 on a restoration was carried out. This was heavily funded by the (Protestant) King Frederick William III of Prussia, probably part of political PR campain, as the (Catholic) "Rhine Province" was the westernmost province of the Kingdom of Prussia since 1822. (Frederick William IV funded as well the completion of the Cologne Cathedral).
This is the reason, why the church today is an interdenominational church ("Simultankirche") used by Roman Catholics and Protestants.
I learned from the timetable outside, that from 8.00 - 10.00 and from 13.30 - 15.30 it is "Protestant", all other times it is "Catholic".