The listed coordinates will bring you to a historic marker for Jerry's Pit, near the Alewife MBTA station (commuter + red lines). The cache is in a park that is a 10-15 minute walk from there. BRING YOUR OWN PEN.
To find the cache you must solve a 16x16 Sudoku puzzle (an UberDoku). It's just like a normal Sudoku puzzle, only bigger. You need to place one hexadecimal character {0123456789ABCDEF} in each square, so that every row, every column, and every 4x4 box, contains all 16 of these characters. This puzzle has a single solution, and you do not need to make any guesses.
You can check your answers at Geochecker.com.
