Depends what you mean by unexplored. Satellites have taken photographs of the whole surface, but I imagine there are still pockets of remote places where no human has set foot.

Inaccessible mountain slopes, central Antarctica, the land under glaciers, central Sahara, deep jungle, far northern Canada and Russia.

Or, more interestingly, modern cities may still hide secrets. For example, it’s well known that London is built on top of London. Digging anywhere typically uncovers archaeological evidence of past generations. But there are still some places which are off-limits to digging because they are under historic buildings. For example, St Paul‘s cathedral very likely has historical artefacts underneath it, but we will never know because you’d have to demolish St Paul’s first to get at them.