Over half a dozen residents of this San Francisco 'castle' have become bitcoin millionaires - take a look inside

The Crypto Castle is a three-story home in San Francisco where young tech workers eat, sleep, party, and plot the future of money.

A majority of the millennial tenants invest in bitcoin, a new kind of payment system that allows people to buy things and send money with anonymity. There are no banks or middlemen. Transactions are recorded on a digital ledger called a blockchain.

Cryptocurrencies (of which bitcoin is the most popular) have been on a tear in 2017. Bitcoin surged in value from about $200 per token in 2015 to above $4,000 in August. Some believe the digital payment system is headed for a bubble that's destined to pop.

"Over a half-dozen people in the time they've lived in my house have become millionaires as a result of crypto," said Jeremy Gardner, a 25-year-old entrepreneur and investor.

In 2015, Gardner, the then-director of operations at Augur, a market forecasting tool that runs on the blockchain, put down a $20,000 deposit to rent the house. It's become a landing pad for people working in cryptocurrency-related tech.

Here's what it's like to live in the Crypto Castle among newly minted millionaires.