I run theatre of the mind, often somewhat improvised. Exploration is hard, particularly if you want there to appear to be any logic involved.

I use a very broad rule for myself, excepting dungeons. Any location should have three branching exploration options at most three levels deep. That means you can fully explore a location in at most 9 rooms. A branch should proceed thematically, and I will often wing it. Not every room needs and encounter, but every room should be interesting. Rely on senses other than sight to add flavour.

Example: a mad wizard's cottage in the woods. Description: "you enter the foyer, and there is a door to either side, and stairs leading up to a mezzanine. You can smell something dank from the left door and you can see some bookshelves at the back of the mezzanine. The right door appears unremarkable."

It's entirely trivial now for the players to decide where they want to explore. Three branches. The unremarkable door can be a bedroom or storage closet or something. The stinky door can be a kitchen that was left untidy and became mouldy, with a backroom that leads to an overgrown greenhouse now home to a shambling mound. The mezzanine can be a library with a workshop behind yet another door, and a hidden door behind a bookshelf going to a room that only contains a standing mirror.

Fuck, this sounds interesting. Wizard has been gone for a while, where? Maybe through the mirror? What was he working on? Etc.

In a four hour session, we'll be lucky to get through two or three such locations, depending on whether combat is involved. Over time, I assemble larger threads from almost entirely improvised beginnings, so I can make callbacks.