Typical flowers and leaves and a square stem. Surely the smell would tell you, but for variety, you might visit Well Sweep Farm, if it still exists, and realize the huge variety of useable culinary mint out there.
Visited it once, a lifetime ago, but found it on the web, recently.

I believe it is a Horehound

Here is a link that might be useful: Gardens Ablaze Horehound

IME mints tend to flower at the end of a stalk, not around the stems or in leaf axels. I think not a Mentha,

What Does it smell like...?

There are Metha spp. with axillary flowers, for example M. canadensis and M. arvensis. The former smells a bit like peppermint, the other more fruity.