Investing $300K in cryptocurrencies is a significant decision that requires careful consideration. Cryptocurrencies can be highly volatile, so it's essential to approach them with caution and conduct thorough research. Diversifying your investment across established cryptocurrencies with solid track records, such as Bitcoin and Ethereum, could be a starting point. However, it's important to note that investing in cryptocurrencies involves risks, and there are no guarantees of multiplying your money. As for predicting which markets may face challenges in the coming years, it's impossible to accurately foresee such outcomes. It's advisable to consult with financial professionals and stay updated on market trends for informed investment decisions.