The further extension to Sofia Airport comprising two underground and two overground stations and a length of 4 kilometers began in 2013, Public Procurement Agency Portal - L1 N. Branch Construction Positions 1 & 2 Public Procurement Agency Portal - L1 N. Branch Construction Position 3 Public Procurement Agency Portal - L1 N. Branch Supervision and was completed on 2 April 2015 at the cost of BGN 136,757,630 (EUR 69,923,066), VAT exclusive.