While Kutná Hora was producing silver, I don't think that this commodity or any other commodity (and surely not one stolen from a colony – colonies didn't really exist) was the main driver behind the glory of the Golden Era – although the silver was obviously needed for our hard currency, the Prague Groschen (picture below). The true reasons were organizational and political, I think, and the character of the economic development was modern and diverse.
Charles IV (1316-1378) is considered by Czechs to be the most stellar ruler of our feudal history, due to the power he brought to the Czech kingdom and that was never quite repeated although Rudolph II who also ruled from Prague (but wasn't quite Czech...) came close (especially when it comes to his support of arts and sciences, something in which Prague has surely lost all of its prestigious status after Rudolph II).
One must understand that he wasn't just a Czech king. Since 1355, he was also an undisputed only Holy Roman Emperor (he was a disputed one, a de facto emperor, for many years before that) and during his reign, I believe the whole reign, Prague was the capital of the whole Holy Roman Empire.
This makes a difference because the Roman Empire has been the traditional brand for the modern type of wealth. You may appreciate how much Vienna has benefited from its being the capital of the Austrian monarchy for many centuries. Similarly, Brussels may have some extra advantage by being the capital of the confederation known as the EU: lots of business revolves around the politicians and administrators. However, being a capital of the Holy Roman Empire might have been an even bigger deal. I suppose that some "taxes" were flowing to Prague from the whole empire.
There were various accidental reasons that made this privileged position of Bohemia possible. However, Charles IV improved the political clout of Bohemia by various mostly peaceful acts, especially acts like clever marriages. For his Bohemia where he was a king and which was therefore the "core" of the Holy Roman Empire, he acquired lots of unusual territories in East Germany, big portions of the current Poland, and elsewhere. At one moment, Bohemia almost had access to the Baltic Sea (see the map below), and so on. Be sure that throughout most of our history, we couldn't consider ourselves to be expansionist colonial masters of any sort so this exceptional era fills us with a certain pride (well, much like the Hussite Wars a century later – Hussites are admired even by many conservative Czechs although they were essentially communists, terrorists, and heretics combined into one).
Note that Berlin was one of the cities in the Czech kingdom and all the major cities have had nice and smooth Czech names.
Internally, Charles IV was a great manager. Especially in Prague, he knew how to support construction of new buildings and infrastructure that was meaningful and profitable for the kingdom as a whole. He founded the Charles [himself] University in 1348, built the New Town neighborhood, the Charles Bridge, the initial stages of the St Vitus Cathedral, the Karlštejn Castle, and other things. Prague would be upgraded from a diocese to an archiepiscopate. He often declared contests – I mean tenders – who is able to build something quickly. Marketplaces were actively managed and timing was important.
It's plausible that the climate was more friendly – i.e. warmer – at that time, too (the so-called Medieval Warm Period). It may have helped although it's hard to decide or quantify it. Charles IV switched Bohemia to "wine drinkers" and wine must have been routinely grown even at places of Bohemia such as Prague itself (note there is Charles-IV-founded "Vinohrady" = "Wineyards" neighborhood over there) where it seems implausible today. Of course, one can't be sure whether it tasted really well and whether it was sweet enough. There were also some protectionist policies against wine importers. 10% of the sold wine went to the landlord and each winery had to send 30 liters to the king, too. ;-)
Prague was the 2nd largest European city in that time and relatively speaking, the kingdom was doing very well. I am not sure whether the Golden Era was so supernaturally golden in the absolute sense so that one would have to search for some particular material cause of it.