Disclosed is a core drill comprising: an external pipe; a coring bit to be rotated by rotation of the external pipe to drill a coring hole and form a core having a core diameter; and an internal coring pipe (1), mounted within the external pipe, to receive a core formed by the coring bit, the internal coring pipe comprising: an internal tubular wall (2) defining a cavity (4) having a diameter substantially the same as the core diameter within which to retain a core formed by the coring bit, one or more viewing openings (8, 9, 10) being formed through the internal tubular wall; and an external tubular wall (3), in which the internal tubular wall is housed coaxially, the internal and external tubular walls being connected to each other so as to form a single-piece double-walled pipe.