In Greece's fifth general strike this year, police fired tear gas as they were pelted with pieces of broken masonry by a few dozen protesters.
Police said seven officers were injured, six people were arrested and two banks and three shops had their windows smashed.
A strong police guard enabled seven tourist ferries to leave Greece's main port at Piraeus, but at least six ferry services were cancelled, the coastguard said, with several thousand travellers unable to sail for the Greek islands.
About 500 union members blockaded ships in the port.
Nearly 50 domestic flights were grounded, while rail access to Athens airport was cut. Inter-city trains also ran a reduced service, as did hospitals, while state offices shut down altogether.
More than 15,000 people took part in protest marches in Athens and Thessaloniki, according to police. Unions said there were 35,000 demonstrators in Athens alone.
People have been angered by the government's latest measure, which raises the general retirement age to 65 for men and women. It was to be discussed in parliament on Tuesday ahead of a vote expected on 8 July.
In Spain, a strike by Madrid metro workers forced millions of residents and tourists to find alternative transport to get to work and the main airport.
Spanish media said it was the first time since 1991 that such a strike had paralysed the metro system, which two million people use daily.
The unions said the 7,500 metro employees would continuing the strike for a third day on Wednesday.
With markets still tense over government debt levels, France's central bank chief said it could take a decade to put public finances right without risking growth.
Asked how long measures to correct French public overspending would last, Noyer told French radio he believed it would take "between five and 10 years.
"Otherwise, if we want to go very quickly, that could have a negative effect on growth. We have to do it progressively, that will take at least five or six years."
Noyer said households feared that taxes would be massively raised, and so were saving money as a precaution.