d = {{#1, #2}, #3} & @@@ Flatten[data, 1] 

or

d = {Most @ #, Last @ #}& /@ Flatten[data, 1] 

e.g.

{Most@#, Last@#} & /@ Flatten[data, 1] // Short 

{{{5., 9.53333}, 0.057735}, <<18>>, {{20., 70.8667}, 0.152753}} 

Edit

Given data allow only for InterpolationOrder -> 1

f = Interpolation[ d, InterpolationOrder -> 1]; 

To visualize data we can make use of various options of Plot3D. To get a better resolution we rescaled z-axis using appropriate values of BoxRatios.

Plot3D[ f[x, y], {x, 5, 20}, {y, 10, 70}, PlotPoints -> 150, MaxRecursion -> 4, MeshFunctions -> {#3 &}, Mesh -> 30, ClippingStyle -> None, ColorFunction -> "DeepSeaColors", BoxRatios -> {15, 60, 5}, ViewPoint -> {-1, -3, 1}] 

d = {{#1, #2}, #3} & @@@ Flatten[data, 1] 

or

d = {Most @ #, Last @ #}& /@ Flatten[data, 1] 

e.g.

{Most@#, Last@#} & /@ Flatten[data, 1] // Short 

{{{5., 9.53333}, 0.057735}, <<18>>, {{20., 70.8667}, 0.152753}} 

Edit

Given data allow only for InterpolationOrder -> 1

f = Interpolation[ d, InterpolationOrder -> 1]; 

To visualize data we can make use of various options of Plot3D. To get a better resolution we rescaled z-axis using appropriate values of BoxRatios.

Plot3D[ f[x, y], {x, 5, 20}, {y, 14, 70}, PlotPoints -> 150, MaxRecursion -> 4, MeshFunctions -> {#3 &}, Mesh -> 30, ClippingStyle -> None, ColorFunction -> "DeepSeaColors", BoxRatios -> {15, 60, 5}, ViewPoint -> {-1, -3, 1}] 

{{#1, #2}, #3} & @@@ Flatten[data, 1] 

or

{Most @ #, Last @ #}& /@ Flatten[data, 1] 

e.g.

{Most@#, Last@#} & /@ Flatten[data, 1] // Short 

{{{5., 9.53333}, 0.057735}, <<18>>, {{20., 70.8667}, 0.152753}} 

d = {{#1, #2}, #3} & @@@ Flatten[data, 1] 

or

d = {Most @ #, Last @ #}& /@ Flatten[data, 1] 

e.g.

{Most@#, Last@#} & /@ Flatten[data, 1] // Short 

{{{5., 9.53333}, 0.057735}, <<18>>, {{20., 70.8667}, 0.152753}} 

Edit

Given data allow only for InterpolationOrder -> 1

f = Interpolation[ d, InterpolationOrder -> 1]; 

To visualize data we can make use of various options of Plot3D. To get a better resolution we rescaled z-axis using appropriate values of BoxRatios.

Plot3D[ f[x, y], {x, 5, 20}, {y, 10, 70}, PlotPoints -> 150, MaxRecursion -> 4, MeshFunctions -> {#3 &}, Mesh -> 30, ClippingStyle -> None, ColorFunction -> "DeepSeaColors", BoxRatios -> {15, 60, 5}, ViewPoint -> {-1, -3, 1}]