4 Dual Lands - Tropical Island, Tundra, Volcanic Island, Underground Sea - that all produce blue mana
All cards are in Very good condition, some shuffling wear visible, so they are listed as Light Play
Buying each one by itself would easily set you back $2,500, but this set of four rare Revised Duals is priced to sell!
Look for my other Dual sets that feature lands for the other four colors.