Internally stiffened composite panels and associated manufacturing methods. An internally stiffened composite panel can include a first face sheet, a second face sheet offset from the first face sheet, and at least one core portion sandwiched between the first and second face sheets. The composite panel can further include a stiffener disposed between the first and second face sheets adjacent to the core portion. The stiffener can have a first attachment portion attached to the first face sheet, a second attachment portion attached to the second face sheet, and an intermediate portion extending between the first and second attachment portions. One or both of the first and second attachment portions can be configured to engage a fastener, such as a blind fastener, for attaching a part to the composite panel.