You can use Plot3D

sol = u /. First@NDSolve[eq, u, {t, 0, 10}, {x, -10, 10}, MaxStepSize -> 0.1];

Plot3D[sol[x, y], {x, 0, 10}, {y, -10, 10}, PlotPoints -> 50]

You can use Plot3D

sol = u /. First@NDSolve[eq, u, {t, 0, 10}, {x, -10, 10}, MaxStepSize -> 0.1];

Plot3D[sol[x, y], {x, 0, 10}, {y, -10, 10}, PlotPoints -> 50]

Or

data = Table[ sol[x, y], {x, 0, 10}, {y, -10, 10}];

ListPlot3D[Transpose@data,
 Mesh -> None,
 InterpolationOrder -> 0, 
 ColorFunction -> "Rainbow"]