What case does the preposition 'in' take?

If you are wanting it to mean 'to' or 'towards', then the Latin preposition 'in' takes the accusative case. For example in domam curro = I am running into the house.
If you want it to mean 'in' or 'on', then the Latin preposition 'in' takes the ablative case.For example in litore sedeo = I am sitting on the shore.