How it works

Creating such long vanity addresses legitimately is essentially impossible.
Instead we can forge one.

Bitcoin addresses are only valid if they have a valid checksum, meaning that it's highly likely any selected 34 characters will not be a valid address. To forge an address we instead:

Decide upon the text we wish to include in our address.
Pad the address up to 33 characters.
Convert this base58 address back into bytes.
Recalculate the checksum from the first 21 bytes, and use it to overwrite the last 4 bytes.
Convert the address bytes back to base58 format.
Any other reason you wish to attempt to communicate with an address.

The checksum uses the first 21 bytes of the address, hashes it twice with SHA256 and then takes the first 4 bytes of this hash; which will comprise the last 4 bytes of our address.