It's a personal opinion; you can consider index and bond funds. It's the best choice for you to make a wonderful long-term diversification investment for your portfolio. The low fee is also a factor that you can keep in mind while considering index funds, which means more money in your pocket. The potential drawback that I found about them is their passively managed nature. Hands-off investing is inexpensive in general, but in an inefficient market, it can be suboptimal. With active management, you can easily deal with it.
One of the more creative solutions I provided was when a client wanted to diversify his investment portfolio; I opened his eyes to the concept of impact investing in local startups focused on sustainable technology. Instead of staying in traditional asset classes, we identified promising startups working in green technology and matched them with this particular client's value of environmental responsibility. We really organised something on a small scale, like a venture capital fund, among other similarly thinking investors. There it provided diversified risk and gave the potential for significant returns. This diversified their investment portfolios in the process but also provided personal and financial fulfilment in seeing that it really contributed to positive environmental change and innovative local businesses.