While "approaching unnoticed" may seem like a straightforward description, there are several synonyms that can add variety to your writing and better convey the sense of stealth and subtlety. For example, you might describe something as "sneaking up," "creeping closer," or "advancing stealthily." Other options include "slipping up," "moving quietly," or "stealing near." These synonyms can be particularly useful in tense or suspenseful situations, when the element of surprise is important. By choosing the right word to describe an approaching object or person, you can create a more vivid and engaging scene for your readers.