Topological gravity is the reduction of general relativity to flat spacetimes. A lattice model describing topological gravity is developed starting from a Hamiltonian lattice version of theory. The extra symmetries not present in gravity that kill the local degrees of freedom in theory are removed. The remaining symmetries preserve the geometrical character of the lattice. Using self-dual variables, the conditions that guarantee the geometricity of the lattice become reality conditions. The local part of the remaining symmetry generators, that respect the geometricity-reality conditions, has the form of Ashtekar's constraints for GR. Only after constraining the initial data to flat lattices and considering the non-local (plus local) part of the constraints does the algebra of the symmetry generators close. A strategy to extend the model for non-flat connections and quantization are discussed.