CREATE TABLE table_204_821 (id DECIMAL, "speed [km/h  ( mph ) ]" TEXT, "train" TEXT, "type" TEXT, "location" TEXT, "date" TEXT, "comments" TEXT)

where was the location for the fastest test done ?
SELECT "location" FROM table_204_821 ORDER BY "speed [km/h (mph)]" DESC LIMIT 1
SELECT "location" FROM "table_204_821" ORDER BY "speed [km/h (mph)]" DESC NULLS LAST LIMIT 1