Exploration on contains 160 cards, counts as 1 expansion for up to 2 kingdoms (since there is so much to explore, 2 different kingdoms may use the same expansion set of cards. This is not required, just a possibility). It will offer almost endless exploration, even if you take it as your first expansion, and it is the richest of all expansions if you want more cards and grow your kingdom size. Note, though, that it is quite expensive in terms of resources needed to do well.