The diggerwasp Crossocerus annulipes  is not difficult when it comes to finding a nesting spot. They can be found on all kinds of location as long as there is some soft wood they can tunnel in. They seem to prefer an entrance in the shade or covered in a cavity in the wood.
This female had found a borehole in old wooden fence planks that were used to build a planter from where she started boring here nest horizontally in the plank.
References1 Nederlands Soortenregister