Write a story about an unassuming antique store with a weird secret.

I think I’m going to exchange antique store for a charity shop. The idea is that the items in the store look like every day disgarded rubbish, and they are disgarded – but not quite in any manner that could be considered usual. Beneath the charity shop exists stone steps that descend downwards almost infinitely, punctuated by the fallen remains of an ancient civilisation. The old ladies (whose job it is to sort through donations to the store) make ventures down these steps and return with items entirely inhuman, alien in origin – which transform themselves as they are brought to surface level, into the regular kind of items that populate the store – and are bought, as bargain finds and disseminated into the wardrobes and living rooms of the stores varied customers. Clear lovecraft influence on this one.