A method of inspecting a flooded cavity within a structure, said cavity being defined by a wall having a wet side interior to the cavity and an opposite, dry side exterior to the cavity; the method including: providing a plurality of parts including at least a connection body, a valve apparatus, a penetrator apparatus, and an inspection apparatus, and assembling together respective ones of the parts in respective use positions thereof to form a pressure retaining assembly, the pressure retaining assembly including at least the connection body and defining a pressure retaining compartment; the connection body defining first and second intercommunicating apertures (23, 24); the valve apparatus including at least a valve, the valve being operable to selectively open and close a valve orifice; the penetrator apparatus including at least a penetrator tool; the inspection apparatus including at least an inspection tool; and further including sealingly fixing the connection body at the first aperture in its use position to the dry side of the wall of the flooded cavity in a floating condition of said structure wherein said structure is floating and at least partially submerged in a body of water in fluid communication with the cavity so that the wall excludes the water in the cavity from a dry interior space within the structure and the wet side of the wall is exposed to fluid pressure within the cavity, so that the connection body forms in its use position a base portion of the pressure retaining assembly; and in the use position of the connection body and the penetrator apparatus and the floating condition of the structure, operating the penetrator tool within the pressure retaining compartment to form an opening in the wall of the flooded cavity within the first aperture so as to establish fluid communication between the flooded cavity and the pressure retaining compartment via the opening; and further including, in the use position of the valve apparatus and the inspection apparatus and the floating condition of the structure, arranging the valve to control fluid communication via the second aperture of the connection body so as to selectively isolate the inspection tool from fluid pressure within the pressure retaining compartment; and after forming the opening, in the floating condition of the structure, advancing the inspection tool through the open valve orifice, the connection body and the opening into the flooded cavity and inspecting the cavity; and then, in the floating condition of the structure, withdrawing the inspection tool back through the opening, the connection body and the valve orifice and closing the valve; and further including, after fixing the connection body to the wall and before forming the opening, pressurising the pressure retaining compartment to a test pressure. providing a plurality of parts including at least a connection body, a valve apparatus, a penetrator apparatus, and an inspection apparatus, and assembling together respective ones of the parts in respective use positions thereof to form a pressure retaining assembly, the pressure retaining assembly including at least the connection body and defining a pressure retaining compartment; the connection body defining first and second intercommunicating apertures (23, 24); the valve apparatus including at least a valve, the valve being operable to selectively open and close a valve orifice; the penetrator apparatus including at least a penetrator tool; the inspection apparatus including at least an inspection tool; and further including sealingly fixing the connection body at the first aperture in its use position to the dry side of the wall of the flooded cavity in a floating condition of said structure wherein said structure is floating and at least partially submerged in a body of water in fluid communication with the cavity so that the wall excludes the water in the cavity from a dry interior space within the structure and the wet side of the wall is exposed to fluid pressure within the cavity, so that the connection body forms in its use position a base portion of the pressure retaining assembly; and in the use position of the connection body and the penetrator apparatus and the floating condition of the structure, operating the penetrator tool within the pressure retaining compartment to form an opening in the wall of the flooded cavity within the first aperture so as to establish fluid communication between the flooded cavity and the pressure retaining compartment via the opening; and further including, in the use position of the valve apparatus and the inspection apparatus and the floating condition of the structure, arranging the valve to control fluid communication via the second aperture of the connection body so as to selectively isolate the inspection tool from fluid pressure within the pressure retaining compartment; and after forming the opening, in the floating condition of the structure, advancing the inspection tool through the open valve orifice, the connection body and the opening into the flooded cavity and inspecting the cavity; and then, in the floating condition of the structure, withdrawing the inspection tool back through the opening, the connection body and the valve orifice and closing the valve; and further including, after fixing the connection body to the wall and before forming the opening, pressurising the pressure retaining compartment to a test pressure.