Svyelunite Temple

Strip away the framing and this is a land pretending to be a slow mana rock: ordinary blue fixing on the front end, with a sacrifice clause that trades the land's continued existence for a one-shot burst of two blue. That second ability carries the design, and the sacrifice is the structural pressure valve that justifies the doubled output. You cannot get the spike and keep the source, so the card forces a real choice between durable mana and a single explosive turn. The enters-tapped clause taxes the front end so the back-end ramp does not come free, a balancing instinct lands of this era leaned on heavily before designers had refined cleaner trade-offs. What keeps the design a footnote is that the math rarely favors the sacrifice: surrendering a permanent land for one extra blue mana, once, is a steep rate most decks never want to pay. Fallen Empires built one of these for each color (white, blue, black, red, and green each got the same enters-tapped, sacrifice-for-double-mana frame), and the temple sits in a lineage of color-pumping sacrifice lands the game would keep revisiting in tighter forms, an early sketch of an idea later printings executed with more discipline.