Hügelkultur raised bed

My BF was nice enough to dig 12" deep hole under our new raised bed.  We loaded it up with a tree we recently cut down.  Great way to fill half of the 17 1/2" deep raised bed with free dirt  Gonna go buy some compost today to fill the rest.  Will mix in some peat and some compoast from my bin for the top layer.  We pushed the dirt with sod between the logs.  Then put a 8" or so layer of twigs.  Then filled it up about half way with the dirt we had dug up.

Does it look good?  Okay to dig down below ground level for hugelkultur?  Most examples I see have logs just sitting on top ofthe ground.

It looks awesome! There are lots of people who dig down as step one of hugel building, and in some ecosystems, most of the bed is underground. There are plenty of factors.

Although I don't normally dig down, I do add lots of wood to my raised beds to act like a moisture sponge and eventually turn into dirt.

The following picture is a little blurry, but it shows the bed I'm currently filling with the Step 1 punky logs in the bottom. This bed is ~30 inches tall and its twin in the background has small stumps and dead planks in the bottom. Both beds got biochar, Duck/chicken shit inoculated wood-shavings, and finished compost on top. The new one with the logs even scored a couple of bins of Okara from a friend, layered into the mix. It's now a few buckets away from full.

One thing I would suggest you consider with your bed if available are some planks flat on the ground against the side of the walls to slow grasses from sneaking in under the edge. The planks can be lifted for weeding, provide edging for when you have to mow, and will eventually biodegrade into soil. My new bed is using some old fence boards (untreated) and I've also used Pallet planks so long as the pallets have "HT" for "heat treated" on them, rather than anything nasty.