  We observe a weakly allowed optical transition of atomic ytterbium from the
ground state to the metastable state $4f^{13}5d6s^2 \: (J=2)$ for all five
bosonic and two fermionic isotopes with resolved Zeeman and hyperfine
structures. This inner-shell orbital transition has been proposed as a new
frequency standard as well as a quantum sensor for new physics. We find magic
wavelengths through the measurement of the scalar and tensor polarizabilities
and reveal that the measured trap lifetime in a three-dimensional optical
lattice is 1.9(1) s, which is crucial for precision measurements. We also
determine the $g$ factor by an interleaved measurement, consistent with our
relativistic atomic calculation. This work opens the possibility of an optical
lattice clock with improved stability and accuracy as well as novel approaches
for physics beyond the standard model.
