Underground passage

There is the ancient legend about underground passage from Narva fortress to Ivangorod. It was digged out by dignified knight Borengaupt for task to rescue his son kidnapped by evil Russians, which hid him in Ivangorod. Many historians, archaeologists, enthusiasts and adventures tried to find it, but all in vain. And now... I've found it! ... or may be something alike... The cryptic passage in Victoria bastion dives under the river and goes in the heart of darkness. I've tried to explore it but lost my courage soon because of lack of food and reserve electric batteries for my light...