Adding subplots to a subplot

You can nest your GridSpec using SubplotSpec. The outer grid will be a 2 x 2 and the inner grids will be 2 x 1. The following code should give you the basic idea.

import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec

fig = plt.figure(figsize=(10, 8))
outer = gridspec.GridSpec(2, 2, wspace=0.2, hspace=0.2)

for i in range(4):
    inner = gridspec.GridSpecFromSubplotSpec(2, 1,
                    subplot_spec=outer[i], wspace=0.1, hspace=0.1)

    for j in range(2):
        ax = plt.Subplot(fig, inner[j])
        t = ax.text(0.5,0.5, 'outer=%d, inner=%d' % (i, j))
        t.set_ha('center')
        ax.set_xticks([])
        ax.set_yticks([])
        fig.add_subplot(ax)

fig.show()