All good suggestions
In general the Greeks are friendly and generous although some Taxi drivers are dishonest so use caution.
The Gypsies, Albanians and African immigrants have a reputation for being thieves. The fake designer label stuff they sell is rubbish.
I'm sure they're not all bad but again just be aware.
And like always be careful when travelling overseas. Don't wear flashy jewellery and only have enough money in your wallet for that day. (the hotel safe is a good place to store valuables)
The Trannys come out at night and they are a site to behold. (Think Greek men dressed as women
)
If you get in trouble, the cops will help although they may be further motived with a small bribe.
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The newish subway in Athens is interesting. You can see parts of the "old city" through glass walls. When it was excavated a lot was discovered and preserved.
Of course the Acropolis and surrounding area is certainly worth a look but there are many ancient sites throughout the city. It's also a great place to just walk around but not alone.