I was in the Street of the Goldsmiths where, in the Middle Ages, those who were skilled
in alchemy burnt the philosopher’s stone
and poisoned the moonbeams
Ewald Murrer. The Diary of Mr. Pinke

Two of the other most famous alchemists of Rudolph II’s reign were the alchemists John Dee from England and his assistant Edward Kelley (also spelled Kelly in some accounts). Dee is widely regarded as a serous and learned man – in fact he spent a portion of his life as an advisor to Queen Elizabeth I of England, as well as to Rudolph in Prague. There are, however, varying views of Kelly. Most regard him as a renaissance "con man" who tricked people into believing that he could turn base metals into gold. However, some believe that he really did see the future – using a crystal ball – and that he successfully predicted both Mary Queen of Scots’ execution and the attack by the Spanish Armada on the English fleet.

Kelley is rumoured to have lived at a house called The Donkey at the Cradle in Mala Strana at 8 Jansky Vrsek. The house is still there, complete with a very weird staircase., though whether it really was one of Kelley’s homes is debatable.

The period of Dee and Kelley is of particular interest to students of Tarot as it was in Prague that Dee is claimed to have discovered the Necronomicon, later called "The book of Thoth" and used as one of the inspirational texts for Crowley’s famous Thoth pack. This is a concise account:
In 1586, a copy of Wormius's Latin translation surfaced in Prague. Dr. John Dee, the famous English magician, and his assistant Edward Kelly were at the court of the Emperor Rudolph II to discuss plans for making alchemical gold, and Kelly bought the copy from the so-called "Black Rabbi" and Kabbalist, Jacob Eliezer, who had fled to Prague from Italy after accusations of necromancy. At that time Prague had become a magnet for magicians, alchemists and charletons of every kind under the patronage of Rudolph, and it is hard to imagine a more likely place in Europe for a copy to surface.
http://www.flashback.se/archive/necronomicon.html
However, again, this is debatable, as no-one is really sure that the Necronomicon every existed.