Is there a workaround for the 90 day limit in the EU? [closed]

Yes, in principle documents are checked at land borders, sometimes even more thoroughly. There are many details in the Schengen Borders Code on how these checks are to be conducted, what type of lanes, what type of signs, etc. Same thing for ships entering and leaving the Schengen area, all this has been considered carefully. In practice, the borders between Hungary or Poland and the Ukraine or Serbia are certainly policed very intensively as are the Greek borders.

Technically, places like Andorra aren't in the Schengen area and border checks are very lax so that's a land border you may be able to cross. But there is also no airport so that wouldn't help you at all. Before Switzerland joined, the checks there were also hit-and-miss, although in my experience trains and busses were checked more, not less, extensively than, say, cars. I have heard more stories of people getting away with minor overstays or missing stamps at airports in France or Italy than at land borders.

Furthermore, the Schengen Borders Code explicitly puts the burden of proof on you, the visitor. You should actively seek an exit stamp where appropriate or, if you don't have one, prove by other means that you really weren't present in the Schengen area longer than you were supposed to. If border guards feel like punishing you to the full extent of the law, a missing exit stamp is all they need. They don't need to catch you in the act and can still impose a fine or a ban later on (e.g. if you present the same passport on a subsequent visit).

In practice, I am not sure how common it really is. For all I know, for a minor to medium overstay and if you are already on the exit, you might get away with a slap on the wrist or a modest fine but the law really gives border guards a lot of latitude, with a standard of proof well below that of criminal law so you cannot count on this to avoid problems.

This is not a workaround. Your passport will be checked by Schengen authorities on exit even if traveling by rail or bus. If they see that you have overstayed the will likely issue you a fine and or a ban.

If you manage to sneak out of the Schengen area by land/sea with out being caught, then you obviously won't be fined. However, when you next apply for a visa (or even a transit visa, if you need one), then you'll have some very pointed questions to answer.