Submerge an uncooked egg in vinegar.
Wait a few days to a week.
The shell will bubble as the vinegar reacts with the calcium carbonate in the shell, releasing carbon dioxide gas:
CaCO3 + 2CH3COOH -> Ca(CH3COO)2 + H2O + CO2
The hard shell reacts away completely, leaving the egg surrounded just by the outer membrane.
The egg is soft, but still intact.