  We describe the design and performance of a scanning tunneling microscope
(STM) which operates at a base temperature of 30 mK in a vector magnetic field.
The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution
refrigerator that contains a vector magnet allowing for fields up to 9 T
perpendicular and 4 T parallel to the sample. The STM is placed in a
multi-chamber UHV system, which allows in-situ preparation and exchange of
samples and tips. The entire system rests on a 150-ton concrete block suspended
by pneumatic isolators, which is housed in an acoustically isolated and
electromagnetically shielded laboratory optimized for extremely low noise
scanning probe measurements. We demonstrate the overall performance by
illustrating atomic resolution and quasiparticle interference imaging and
detail the vibrational noise of both the laboratory and microscope. We also
determine the electron temperature via measurement of the superconducting gap
of Re(0001) and illustrate magnetic field-dependent measurements of the spin
excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin
resolution by imaging the magnetic structure of the Fe double layer on W(110).
