  Motivated by the recent progress in the effective string description of the
interquark potential in lattice gauge theory, we study interfaces with periodic
boundary conditions in the three-dimensional Ising model. Our Monte Carlo
results for the associated free energy are compared with the next-to-leading
order (NLO) approximation of the Nambu-Goto string model. We find clear
evidence for the validity of the effective string model at the level of the NLO
truncation.
