胡同 is believed to come from Mongolian 'hottog' meaning 'water well' — settlements formed around wells during the Yuan Dynasty. The hutongs of Beijing are a UNESCO-recognized cultural heritage.
grammar
The 儿 suffix (erhua) is the hallmark of Beijing Mandarin. Without it, 胡同 (hútòng) is the standard form used across China.
usage
走街串巷 (zǒu jiē chuàn xiàng) means to wander through streets and alleys — a common activity for tourists in Beijing's hutong areas.
