Definition: "smooth as a baby's bottom"

This is a container clue - one word or letter goes inside another word to form the answer.

Put the letter 'L' (Left) inside a German word for 'bath' that you might see in spa town names like Baden-Baden.

Answer: BALD | 'L' (Left) goes inside 'BAD' (German word for 'bath', as used in spa town names) to give BALD, meaning smooth as a baby's bottom.