The point of getters and setters is to avoid exposing internal state to the outside. In this way you're not getting direct modification of fields, you're sending a signal: "hey Date object, get me your representation as an integer number of seconds since epoch", the outside doesn't care whether the Date internally uses the seconds since epoch representation, or whether it translates to this representation just for this method.

Getters / Setters don't automatically mean that the internal state of an object is exposed. For example, an object may internally have mutable linked-list of something, but a Getter that returns an array (immutable) of immutable members.

What is the alternative to Getters / Setters (or, properties, which is basically just syntactic sugar) in an OO language?

That's being way too dogmatic.

The problem with taking encapsulation to an extreme is that you are trading off against flexibility. The more you hide your state the less any external party can implement their own logic using that state, and the more separate concerns have to be bundled into the class hiding the state because they can't be dealt with anywhere else. Everything in software design is a tradeoff.