One of the first to record the oldest Karlovy Vary legend about the discovery of the geyser known as the Sprudel by Charles IV was the renaissance physician Dr Fabian Sommer, a native of Karlovy Vary. In his book on the use of Karlovy Vary's waters from 1571, he relates the story thus:

"It is said that Charles IV once went hunting in the woods, in the hilly areas and valleys where now the hot springs do bubble up. The woods in this place were full of game. During the hunt, one of the hounds started to run after an animal. Whilst following it, the hound fell into a pool where hot water does now burst from the ground. The hound began to howl in pain. The hunters ran to the hound, believing it to have been wounded by the animal it had been chasing. The marvel which they saw amazed them greatly. They stepped closer, pulled the hound from the pool, and then tasted of the hot water which had so distressed the hound.

The entire event was reported to the Emperor Charles IV, who then went in large company himself to marvel at this singular wonder of nature. In the presence of his physicians, the wise ruler said that such hot water may drive off many grave ailments, and that it was beneficial and invigorating. Then he himself used the water (it is said that he had an afflicted leg), and sensed assuagement and improvement. The ruler was overjoyed at this, and soon gave orders that the whole place be settled, and that around the springs, houses be built. The place where the Emperor used that water was, according to information, in that place where once stood the municipal bath and where the guildhall now stands. At that place the spring wells up whose waters do not burst forth excessively, and are but warm. It is related that in this place, many years ago, a seat was cut into the rock on which the ruler sat, and wherefore it was named the Seat of the Emperor Charles. And yet this place is no longer to be found, and on it the guildhall has been built.

After the water had effected its cure on him, the Emperor Charles had a new town built on this spot. He wanted it to be walled about for protection, but his intents were thwarted by yet more pressing happenings. That it should be so can be seen up to this day from the fragments of protective wall which are under the Deer Rock. On this Deer Rock many collapsed cellar vaults can also be seen. Aged citizens do say that it was the intention of the Emperor Charles to build on the said hill a castle for the protection of Karlovy Vary. Even the name of the town bears witness to its discoverer, for it is named the bath of the Emperor Charles, Karlovy Vary."