You can buy and trade cryptocurrencies primarily on online exchanges. To be clear, active trading of cryptocurrency is technically not considered a passive income stream (because you have to spend a significant amount of time monitoring the market closely). Still, significant buy-and-hold opportunities have helped many people earn upwards of $10,000 monthly for years.
During 2011, bitcoin (BTC) had a sudden price increase of over 3000% in just a few months. Imagine the passive income you could have made if you bought BTC at $1 and sold it at its peak. Moreover, BTC prices have had many explosive bubbles that gave people massive opportunities to build wealth over the past years.
Since 2020, Bitcoin's growth rate has slowed considerably, but it is still one of the last decade's fastest (and most consistently growing) investment opportunities. From January 2020 to December 2020, BTC had a 224% increase in value. In March 2021, Bitcoin hit nearly $60,000USD. Multiple well-known individuals have made predictions that BTC could be worth $200,000 by 2025 while 1 to 10 million USD by the end of 2040, which would be a tremendous passive income opportunity if capitalized on now.
Another crypto growth example is Ethereum. Right after creation, ETH had a cost of just under 67 cents per coin. However, with its steady rise over the last few years, ETH now routinely peaks at over $3500. Experts have predicted that it may reach over $100,000 per coin by 2023.
Other cryptos such as Litecoin have also seen dramatic price rises since their releases. In particular, Litecoin went from just a few cents in 2011 to more than $200 in 2017. It has certainly had its ups and downs over the years - now sitting in the neighborhood of $168 - but despite its current situation, many cryptos enthusiasts predict that it may eventually reach upwards of $1000 per coin by 2030.