The second MoEDAL Apparatus for Penetrating Particles (MAPP-2) is proposed for deployment at the High-Luminosity LHC (HL-LHC), comprising a large instrumented tunnel decay volume adjacent to Interaction Point 8 (IP8) with a volume of 1200 m$^{3}$. The detector utilizes large-area scintillator panels with 𝑋–𝑌 wavelength-shifting fibres read out by silicon photomultipliers arranged in a “Russian Doll” configuration to measure the displaced vertices of long-lived particles (LLPs) emanating from IP8. The detector incorporates a radiator layer to also allow the registration of photons in the final state. The sensitivity of MAPP-2 is complementary to other planned LLP detectors and the existing LHC general-purpose detectors. We present a few physics benchmarks to illustrate this sensitivity. The initial plans for deploying the MAPP-2 detector at the HL-LHC were endorsed by the LHC Experiments Committee (LHCC). A Letter of Intent to be submitted to the LHCC is under preparation.