To date, half a dozen DLAs have been detected in GRB afterglows, but most have modest signal-to-noise ratios. Our detection of a DLA in the afterglow of GRB 030323 is unambiguous: its neutral hydrogen column density is log N(HI)=21.90$\pm$0.07, higher than any (GRB- or QSO-) DLA HI column density inferred directly from Ly$\alpha$ in absorption. We discuss several other properties such as the metallicity, the detection of fine-structure lines of SiII, and our strong upper limit on the H$_2$ content. The GRB afterglow allows us to infer all these quantities, even with the host being as faint as V=28. The successful launch of the Swift satellite (November 2004) has made high-resolution spectroscopy of a large sample of GRB afterglows possible. This will offer a unique way to study in detail the interstellar medium inside GRB host galaxies as a function of redshift.