Extending chwhite and WW:
The board is a Colony board with all 8 of the VP kingdom cards, and Black Market (and one other). The BM deck contains Trade Route and King's Court at the least. The game has 3 players: you and two extremely bad AIs that seem to purchase nothing. You have bought out the Islands, used a KC from the BM deck with each Island, and meticulously set aside 36 cards--26 single unique cards from the BM deck and the board, 10 Gardens, and 12 Islands; none of the cards is a Fairgrounds or a Trade Route. Your mat contains, therefore, 28 total unique cards, and 48 cards total.
In your hand is a single Trade Route (29th unique card, 49th total). When you play it, you get $12 to spend and an extra buy. You purchase two Fairgrounds. This gives you 30 unique cards, making each Fairground worth 12 points--a 24 VP gain. It also gives you 51 total cards, increasing the value of each Gardens by 1 VP, for 10 VP. Total VP gain: 34 VP.