A seal having a first seal mechanism adapted for insertion between a first structure and a second structure, wherein the first structure is in communication with a first medium and the second structure is in communication with a second medium. The seal also includes a second seal mechanism, which is pressuringly biasable against the first seal mechanism and against the second structure by the second medium. In certain embodiments, a system has a first structure in communication with a first medium and a second structure houses a seal assembly between the first and second structures. The seal assembly includes an interface seal disposed against the first structure and a flexible seal pressuringly biased against the second structure and the interface seal by a second medium.