We use HST spectra of AGN to study the gas inside and outside galaxy halos. These studies reveal that galaxies have extended (300 kpc) radius halos, which blend into the general intergalactic medium. I will show the first results of our study of the properties of the gas as function of location in the galaxy halos. I will also summarize a study of 24 AGN that provide the first 2-D view of a 30x6 Mpc filament at cz~3500 km/s. The baryonic mass inside filament galaxies is 1.4x10^13 Msun, while the mass of filament gas outside galaxy halos is found to be 5.2x10^13 Msun. We show that the gas is concentrated near the filament axis, but also that the simulations overpredict the detection rate between 2.1 and 5 Mpc from the axis.