  We present an atomic resolution scanning tunneling spectroscopy study of
superconducting BaFe$_{1.8}$Co$_{0.2}$As$_2$ single crystals in magnetic fields
up to $9 \text{Tesla}$. At zero field, a single gap with coherence peaks at
$\overline{\Delta}=6.25 \text{meV}$ is observed in the density of states. At $9
\text{T}$ and $6 \text{T}$, we image a disordered vortex lattice, consistent
with isotropic, single flux quantum vortices. Vortex locations are uncorrelated
with strong scattering surface impurities, demonstrating bulk pinning. The
vortex-induced sub-gap density of states fits an exponential decay from the
vortex center, from which we extract a coherence length $\xi=27.6\pm 2.9
\text{\AA}$, corresponding to an upper critical field $H_{c2}=43 \text{T}$.
