You may not build excessively long bases.
Your entrance MUST stay within the boundaries of your property or the general area of it. Your entrance must also be reasonably long.
This is an example of a base that fully breaks the rule. The entrance is outside the property and does not stay in the general area of it:

This is an example of an entrance, although inside the property, is still too long of an entrance:

This is an example of an entrance, which is technically outside the property, but stays in the general area of it while also being short:
