Compactifying 6d N=(2,0) superconformal theories on Riemann surfaces yields 4d N=2 gauge theories. The sphere partition function of such a 4d theory is equal to a CFT correlator on the Riemann surface. The correspondence can be enriched by including half-BPS operators of codimension 2 or 4 in the 6d N=(2,0) theory. Depending on their orientation, these become loop operators, surface operators, or domain walls in the 4d theory. I will describe the surface operators as 2d N=(2,2) gauged linear sigma models coupled to the 4d N=2 theory. This forms a microscopic description of the intersection of M5 branes with M2 (or M5) branes. Time permitting, I will propose a 3d N=2 description of the S-duality domain wall of 4d N=2 superconformal QCD, akin to the T[G] theory of Gaiotto-Witten.