The boy had told his parents that he was heading to Slussen, a key transport junction, but when he had not got in touch and did not answer his mobile phone the police were informed.
“He was later found after a friend showed how it was possible to get into the system of tunnels. When the police patrol came as far as a door where the lock had been busted open they decided to go down into the shaft, where they found the body,” Magnus Berntsen at the police told news agency TT.
“It is strange that a door to a 30 metre deep shaft is not welded shut just closed with a lock that can be easily busted open,” he added.
According to the police it remains unclear why the boy was at the location and whether he had been on his own or with a friend. But there is no suspicion of a crime having been committed, Berntsen said.
Slussen is a central road and metro junction in Stockholm named after the locks that divide Lake Mälaren from the Baltic Sea.
Slussen has long been admired as an example of ingenious traffic and urban planning but as it was built before Sweden shifted to right-hand traffic does not work as it was designed. In recent decades it has become progressively more dilapidated and proposals have been submitted for a major redevelopment.