Planting suggestions

I'm looking for ideas for this corner of the garden. Currently it's just a pile of rubble.
to give you an idea of what I'm looking for, i would have liked a rock garden, or a tree fern under planted with a selection of ferns and grasses, but it's a North East corner, so catches a bit of sun during the day.
im not looking for anything too flowery, maybe something architectural, or a collection of the same plant.
the area is about 5ft square, and it can be flat, of I can build over the rubble.
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