Depends on which beach... I wouldn't personally consider it close to any of the nicer beaches. You'd need a car for that. I guess you could take a bus, but that would take a good hour.
Maybe 15-20 minutes
You can (i have - as a British tourist) walk. I would however only do this with my dude friends - not a family There is a tram, which is fun and useful. Also there are a taxis and you did see cyclists
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