  We demonstrate a cavity-based solution to scale up experiments with ultracold
atoms in optical lattices by an order of magnitude over state-of-the-art free
space lattices. Our two-dimensional optical lattices are created by power
enhancement cavities with large mode waists of 489(8) $\mu$m and allow us to
trap ultracold strontium atoms at a lattice depth of 60 $\mu$K by using only 80
mW of input light per cavity axis. We characterize these lattices using
high-resolution clock spectroscopy and resolve carrier transitions between
different vibrational levels. With these spectral features, we locally measure
the lattice potential envelope and the sample temperature with a spatial
resolution limited only by the optical resolution of the imaging system. The
measured ground-band and trap lifetimes are 18(3) s and 59(2) s, respectively,
and the lattice frequency (depth) is long-term stable on the MHz (0.1\%) level.
Our results show that large, deep, and stable two-dimensional cavity-enhanced
lattices can be created at any wavelength and can be used to scale up
neutral-atom-based quantum simulators, quantum computers, sensors, and optical
lattice clocks.
