The first city in Europe I was ever in was Brussels (back before the large-scale influx of Middle Easterners). It seemed like an unfriendly place, but after I had traveled around Europe it didn't seem as bad as some other cities.
I once had a conversation with an American university professor who told me of his experience in Brussels some years ago. He unwisely took a shortcut through a Muslim neighborhood and was lucky to escape with his life. I don't know whether they were Moroccans, Algerians, or a mix of several nationalities.
Also blocks.