It's a bait to get you to attend a high pressure timeshare or holiday 'club' presentation.
There will probably be a processing fee and your free holiday, if it exists at all, has to be taken from an airport of their choice to a resort of their choice at maybe only a week's notice. Turn it down and your fee is lost. You have to attend a further high pressure sales talk in resort.
If you are flexible about travelling and firm about saying NO you can get a very cheap holiday this way but the odds are against it.
That's assuming it's an 'honest' offer and not a total scam.
Holiday clubs are always scams and timeshare marketed in this way is too.