The Hunger Wall gets its name from the idea that it was built in order to provide work for the locals during a serious famine in 1361. While the construction of the wall certainly did afford work during the famine, its real purpose was strategic and it provided protection for the castle and Mala Strana against attacks from the west and the south. Originally the wall was 4-6 metres high, about 2 metres wide and equipped with battlements and bastions. The final bastion (it is assumed there were 8 originally) became the site for the Stefanik Observatory. About 1200 metres of the original wall still remains.
You can walk up Petřin Hill along the side of the wall. It's quite a steep climb but it gives you an idea of how arduous building it would have been! There are easier ways of getting to see it up close - most notably by taking the funicular and then walking across to the wall from the top station.
It's not a good trip out if the weather is bad, but on a fresh winter or spring day it's quite exhilarating and the views across the city are great, even if the origins of the wall are only myths (like so many of the stories about Prague). Apparently the phrase Hladová zeď is now used to describe useless public works...but at least this one has character, unlike our equivalent PFI infrastructure projects in the UK!