The Westdeutsche Allgemeine Zeitung (WAZ) reported that the pair, a young woman and a young man, fell down a 30-metre chimney at about 3 am.
The fall took the couple from the roof all the way down to the cellars of the 18th Century mansion.
Firefighters rushed to the scene and were able to talk to the pair, who were at the base of the shaft, as they entered from entrances at both the top and bottom to come to their rescue.
The rescue workers were unable to give the students first aid on the scene as the chimney was too narrow – just 80 centimetres by 80 centimetres.
“Their life-threatening injuries demanded extensive know-how from the climbing rescue workers,” the fire service said on Monday.
Firefighters had to knock down part of an interior wall in the building to reach the young woman, who had slipped below steel bars projecting across the shaft.
But it still took three hours to get the young couple out of the chimney.
Fire service spokesman Tobias Schülpen told WAZ that the two had climbed onto the cover of the chimney after sneaking onto the roof But the cover gave way and the pair fell down the shaft.
“They fell feet-first into the shaft and may have slowed one another down because of how narrow the shaft is,” Schülpen said.
“The signs don't point to them sitting on the edge of the chimney and then overbalancing.”
Academy students and professors were shocked at the accident, which is likely to overshadow the “Sommerrundgang” - an exhibition when final-year students show off their final projects.
“We hope they survive,” said Academy Chancellor Dieter Koska.