dusk was falling as machiavelli and ezio carried the apple in its box down into the catacombs below the colosseum and , passing through the dreadful gloomy rooms of the remains of nero 's golden house , carried torches before them as they made their way through a maze of tunnels under the old roman forum to a spot near the church of san nicola in carcere , where they found a secret door within the crypt .