Millisecond spin-period radio pulsars provide us with unique astronomical "laboratories" for exploring fundamental physics in a variety of ways -- from the physics of matter at super-nuclear density, to experimental tests of gravity, to the possible direct detection of gravitational radiation. In this talk, I will discuss two such projects: First, our discovery of a two solar mass pulsar, currently the highest well-measured neutron star mass. This places strong constraints on the nuclear matter equation of state at high densities. Second, I will present recent results and future prospects for the ongoing effort to use an array of pulsars as a nHz-frequency gravitational wave detector.