I don't. But I'm no greenhouse expert. Maybe water will intrude down the entrance slope and fill the walking pit?
Water would definitely do that, @John Brunner ….. Good thought ! If you had a little rise in the yard, you could use this idea like they did the old root callers, which were built on top of a small rise so that the door would be lower than the top if the cellar mound. Then , if you put bricks around the entry steps, water would run off, and not go down the steps and into the bottom of the greenhouse. One house that we lived in had a nice attached garage, but it was built lower than the house, and the driveway sloped down towards the garage. Every time it rained, we had water in the garage, so we had to be careful not to store anything on the floor that could be affected by water.
A lot of potential problems, one of which is the water issue. Most of the rest depend on the climate and the soil type where it is built/dug. Here insulation would have to go much deeper, and the bottom of the inside wall of the walkway would have to be more secure at the bottom. It is an interesting concept though. Are you planning to make one @Dwight Ward?
Now that we talk about it, I wonder if exposing the soil face that far down might also increase evaporation and the water rapidly leeching out of the soil.
You and John got the flaw. I'm looking at the design and thinking of variations without the excavated walkway. Without that, though, it looks like you'd just have a normally constructed greenhouse. I'm selling my house so the actual erection will have to wait on me moving to my new property. If I come up with a plan I'll post a drawing. At my latitude I'd only need a foot or so of buried insulation.
I'm thinking of a poly glazed greenhouse built lower than usual over galvanized pipe right on grade. Maybe 6 and 1/2 feet down the middle and narrow enough so you could get to everything from the center walkway. I'm no expert either but that would be easy to put together and cheap. The door would be tricky, though.
I want to downsize. It will be in or close to Federalsburg. I'd like to be in the country where I could have an outside dog.
Not to dissuade you from having fun, but what does a greenhouse in your zone really get you? I've looked at it here and figured it just extends the growing season a month or so. There's a farm nearby that gives classes ($$$$) in herbs & such and they grow some veggies (plus beef & poultry.) They have small greenhouses with wood stoves in them. I think the larger benefit is climate control.
A greenhouse in a moderate location can get you year-round produce, but at the very least it would allow you to start peppers, cucumbers, and tomatoes earlier in the season without having lights and such inside. Climate control is, of course, another big benefit. You would certainly be able to grow lettuce, spinach, and other things year-round even without heat.