One of the largest construction projects of recent years, the tunneling through mountains at the notorious Kakia Skala cliff face on the Athens-Corinth highway, was handed over partially to the public yesterday, in what has become a daily ritual of inaugurations as major projects open in time for the Athens Olympics. In another major development as the Greek capital changes face, the metro line between the city center and Athens airport will open today. Rides will be free today and until midnight Saturday so that people can get acquainted with the route. The special metro trains will come out of their tunnel on Line 3 at the Doukissis Plakentias station, which opened on Wednesday, and continue on the suburban railway surface line to the airport. Rides on the Proastiakos suburban railway will be free from 11 a.m. to 6 p.m. today and from 10 a.m. to 6 p.m. tomorrow and Sunday on the stretch between Larissis Station and the airport. On Monday, the station at Aghios Antonios will link the densely populated suburb of Peristeri to Line 2 in one of the subway’s most significant extensions. The 8.5-kilometer (5.3-mile) stretch at Kakia Skala took six years to complete, suffering delays, changes in plans and budget overruns. The stretch that was handed over yesterday is for Corinth-bound traffic. The two tunnels for traffic headed for Athens will open at the end of the year. In the meantime, Athens-bound vehicles will have a much easier time from the end of next week onward, when they will have the two lanes that outbound vehicles were using until yesterday. It will take a few days for the barrier between the inbound and outbound lanes to be torn down and the road turned into a four-lane highway. The work at Kakia Skala is the last section of the Athens-Corinth highway to undergo major construction and is expected to end bottlenecks on busy days. The tunnels that were handed over yesterday have the widest radius of tunnels in Europe (15 meters) and have three lanes and a service lane. They have a total length of 3,750 meters, with the one at Gerania 850 meters long, the one at Eupalinos 1,700 meters and the one at Aethra 1,200 meters.