Even though the history records of Sigiriya starts with the king Kashyapa, there are many folklore which connects Sigiriya with the long lost ancestors of Singhalese people. According to the folklore the Sigiriya rock was selected for building a palace long before Kashyapa. It is believed the elder brother of Demon King Ravana, Vaisravana built his palace on the rock. Which was developed by Kashyapa as a fortress... this is what I could compile using the folklore and myth...
While my visit to Sigiriya, I was asking myself the question, how can a king who only ruled for 18 years, build and develop a place like Sigiriya? Of cause what we see today is just bits and pieces of what was once a Royal three story palace and a park, complete with fountains, swimming pools and beautiful kiosks. It could be that the King Kashyapa ruled for more than 18 years, and the author if Mahavansa got the timing incorrect. However we have reason to believe this is not the case, simply because the Author of Mahavansa (Venerable Mahanama Thero) actually witnessed the whole story from the Pidurangala temple which is close to the Sigiriya rock itself.
The other plausible explanation is that Sigiriya was already a fortress and most of its architecture was intact when Kashyapa decided it as the venue for his palace. This is where the folklore aligns with the history records. However it should be noted that Mahavansa or any other history book available to date does not describe this fact.
According to the folklore, Sigiriya was known as Alakamanda or Alakamandawa by Singhalese Yakkha Tribes. Alakamandawa was the palace of Kubera (also called Kuwera).
According to Hindu mythology, Kubera (also read as Kuvera), is believed to be the lord of wealth. And Kubera is also believed to be the god-king of the Yakshas. According to Hindu scripts, He could be regarded as a protector of the world and the overload of many semi-divine species. Some of the Vedic texts describe Kubera as the chief of evil spirits, where Hindu epics depict him as a god.
As depicted in this Wiki picture, he is usually depicted as a short, fat man, adorned with jewelery. One or more money bags are also typically present in these depictions.According the hindu scriptures, Kubera rules Lanka, but was overthrown by his stepbrother Ravana. These scripts describe Kubera settling down in a palace and a city called 'Alaka' situated in the himalayas. Alaka is ofted described as a glorious city with many riches. Even today 'Kuwera' is used in Singhaese to denote a person adorned with wealth.The name Kubera is believed to be the culmination of the two Sanskrit words Ku + Vira (Earth + Hero).In Buddhist pantheons Kubera is known as Vaisravana. Vaisravana and Ravana are both sons of demon king Vishrava. Sri Lankan folklore manifests that Alaka is not in Himalaya. It is a common belief that Alaka or Alakamandawa is in fact the Sigiriya citadel.