Listen to the locals

 The best decision I ever made was to listen to the locals. Tripadvisor is good of course but ask the locals what you should do and where you should go, they always know better. 

My best "local finds" were: a nudist beach in Syros (they forgot to tell me it was nudist) and the bunkers of Barcelona. 

If you you ever go to Syros I highly recommend talking to the singers on the streets, a bunch of young hitchhikers going around the different islands playing their music- it's obvious they know the best spots! They're the ones that recommended the beach. I wouldn't be able to give its name because it doesn't have one but here's how you can get there: after Galissas beach climb up to the church (go inside it's beautiful) and then hopefully you'll find someone, like me, that will show you the little hidden path, otherwise just follow the dirt road and eventually you'll see it. (IMPOSSIBLE TO MISS ITS STUNNING) 

And if you ever find yourself in Barcelona you must go up to the bunkers for the sunset. Take the same bus as to go to Parc Guell and it's the stop after that. From there just follow the people going up. If you ever go to Barcelona in August just a quick heads up: you'll hear more French and German than Spanish. And thankfully the bunkers is a very local place where all the youngsters go to drink a Cerveza and eat chips. As soon as the sun sets the speakers are turned up and the music starts, it's just a huge outside (free -very important) party.