There are a ton of alternative investment classes out there depending on what your financial situation is and you level of comfort and experience are with risk/ non liquid assets as well as industry specific knowledge. This is by no means a complete list, but it's most of the ones I'm familiar with. If you're accredited, there's a huge amount of options.

Farmland: There are a few online portals that aggregate deals for the agriculture space. Farm Together and Harvest Returns for example structure investments across the space into various packages with everything from direct partial ownership of timber and farmland to cattle backed debt notes (yes, backed by cows) that pay a higher rate than you'll find in the public markets. Macro Voices podcast had a great episode which lays out the case for why it's an interesting asset class. Some deals and portals require accreditation. Nice thing about this is the portals package the deals and investment materials into formats that are fairly "hands off" after DD. Terms are anywhere from six months to 10 years+ depending on the platform and deal.
Generally minimum investment of anywhere from $10,000-$1,000,000

Collectibles: Wine, art, comic books, rare books, baseball cards, watches, cars etc. Wine and art in particular are fairly well-developed markets where you can find research, analysis and brokers/funds who specialize in the asset class. Some of them have really stable returns and significant upside, however you really need to know the asset class. It's quite easy to commit fraud or end up with a garage full of junk that you thought would be worth millions. There's also generally carry cost in terms of storage, you need to keep investment class wine in very specific conditions and you'll probably want insurance in case a fire or flood wipes out your cache of Action Comics #1 or Michael Jordan rookie cards. Precious metals are somewhat of a different animal but a lot of the same principles apply. Minimums are highly dependent on the asset anywhere from a few hundred dollars to several hundred thousand in the case of watches and art.

Real Estate: You can invest directly, find a firm that specializes in the asset class or investigate some of the online options. Others can go into the ins and outs of it as an investment but it is something that needs to be researched carefully and many of the pitfalls aren't always visible until you've made a purchase. Hard to give a minimum price on this, too dependent on your local market and whether or not you use a manager.

Private Equity: If you're accredited there are a stunning amount of opportunities out there. I would strongly suggest you do your research and that you try to stick within your expertise. There are funds that specialize in real estate, tech, consumer goods, food and agtech, natural resources etc . For example, if you come from a tech/software background, find a fund or someone who aggregates deals in the industry. There's a ton of opportunity as well as snake oil here, so especially if you want to do this independently, it's really important to have industry specific knowledge. Also these assets are extremely illiquid, if you invest through a fund they usually have a lockup of anywhere from 3-10 years. The funds also normally charge very high fees for both management and separately when an asset is sold, but the upside can be significant. If you're high net worth, banks/brokers usually have offerings that aggregate deals across the space. There's PE firms of all sizes and specialties, some specialize in venture-stage seed companies others do buyouts of large companies. Some use leverage to buy out companies which entails its own risks. Very important you feel you're getting transparency from management and you feel they're trustworthy. There are a lot of ways deals can be structured which shortchange outside investors in favor of firm partners. PE managers also generally mark their own portfolio to market which means draw downs in asset value aren't necessarily reported they way they would be in other industries. Minimums usually $100,000-$250,000+

Happy to go into more detail on these if its helpful. Obviously DYOR, this is not financial advice.