The trains between Amsterdam and äirport run every 10 minutes, so you are only a very short ride to one of the worlds greatest cities. It's beautiful and you can see quite a bit in 5 hours. The #20 tram makes a circle and will give you a nice view of the city, and stops at many of the main attractions.
You don't need to be scared as it is a pretty safe city, other than pickpocketing and bike theft, not too much happens. I've walked and ridden a bike in Amsterdam many times alone at night and have not had any problems. Go see for yourself, and dont be scared!
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American living in NL