They have to grope their way down guiding ropes to the sunken ship, on its side on the seabed at a depth of 40m.
They have to struggle through narrow passageways and rooms littered with floating debris in silty water.
Park Seung-ki, spokesman for the Ministry of Oceans and Fisheries, said bedding materials from the ship were found as far as 30km from the disaster site on Friday.
As days go by, personal belongings and debris from the ship have been spotted further and further away, fuelling concerns that strong currents may have swept some bodies into the open sea. As a precaution, recovery workers put rings of netting around the site days ago.
The relatives of those still missing are insisting that all the bodies be recovered before efforts begin to raise the sunken ferry.
The Sewol capsized on April 16 with 476 people on board - more than 300 of them from the same Danwon High School in Ansan city, just south of Seoul.
Public anger and frustration has been amplified through greed and irresponsibility being blamed for the poor handling of the catastrophe.
The captain and 14 of his crew have been arrested.
- AAP