You can do it yourself, but you can do it through intermediaries. You can - under a formal lease agreement, or at your own peril and risk. In addition, apartments are rented for a day or for a long time, after renovation or in the existing state - there are a lot of options.
If the apartment is in the historical center of a metropolis actively visited by tourists or in a resort town, you can make not just a refreshing renovation, but renovation in a European way and get a good permanent profit for renting an apartment.
Sell an apartment or make the "extra space" work for yourself?
It all depends on the specific situation. If you need a large amount at once and there is an apartment inherited by inheritance or in another legal way, but you do not use this apartment, then you can sell it and solve the problem with money without resorting to a loan. If you don't need a large sum right away, renting an apartment is the best way to profit from unused property without losing it.
It is possible to rent an apartment well only in good condition
Strictly speaking, tenants can also be found in an apartment without renovation. But tenants in this case, as a rule, are quite specific. As a result, the rent may not only not bring profit, but also become unprofitable, and the living space itself may turn from housing without repair into an apartment "in a dead state." Therefore, it is better to rent an apartment in a decent form and at least with a minimum set of items necessary for life - a kitchen set, a sofa, a wardrobe, a TV and a refrigerator. And if you arrange your life properly, complementing the "gentleman's set" of furniture, household appliances and utensils with a washing machine, good dishes, a comfortable computer desk and a hallway, the apartment can be rented out not only quickly, but also very profitably.
Does it make sense to rent out an apartment in a bad neighborhood?
Certainly. In addition, if your “extra” living space is not in a very good place and does not suit you as a housing option, then other people, most likely, will not be interested in it as an exchange option without additional payment or purchase for good money. Therefore, if you want to exchange housing not in a prestigious area for another, renting out an apartment is a great opportunity to collect an additional amount after a while and exchange a bad apartment for a better one. In the event that you do not live in an apartment, and you are not going to sell or exchange it, then it is all the more reasonable to rent it out - regardless of how much they pay for it.