you claim the land, you can (and probably should) claim a right of access through whatever land you’re planning on trodding across. Because there is no owner of the other land, there is no need to negotiate – you register the claim with the state, and you’re done.
But the state won’t just let you register any arbitrary parcel of unowned land as yours. Property arises from the fact that you have a right to keep the wealth you create; where there is no wealth-creating effort, there is no property. Undeveloped land is worthless in itself. When you build yourself a home, it is primarily the home that becomes your property; the land it occupies comes along with it as a secondary consequence.
So if you approach your home by plodding through the wilderness on no established path, then what you have earned by building the house is: 1, the house; 2, the land it occupies; 3, a right to access the house over any route you might find. #3 is a secondary consequence just like #2; it means that anyone developing the land around your home must offer you at least one route that is suitable for accessing your home without an increase in costs (in terms of traveling time, muscle effort, etc.).