How to get Letter of Invitation to travel to country?

[Gnits]

Some countries require a visa to enter, invariably these visas seem to need a 'Letter of Invitation'.
How do lone travellers get such a letter when they have no contacts in that country? (or perhaps they can't and that is the whole point?)

For example, I fancied getting the ferry over to Algeria from Spain to just go and have a look about on the motorbike. To do that I need to apply for a visa and that requires a letter of invitation.
I have already spoken to a travel company and they say they can't help.
Mauritania also now needs a visa as of Jan 2025 and the same thing applies.

Is this even possible without huge amounts of effort? Do I need to speak to more travel companies?

[FlyVintage]

An in-country guide/travel organisation will provide the required invitation.

Ahmed Zegri of Mezrirene Adventure is an example (I’m not permitted to add a link but will come up in a search).

Edited to add reference.

Edited by FlyVintage on Saturday 29th March 11:18

[Gnits]

Oooh, that's splendid.
Thanks for that!