This female Symmorphus crassicornis [1,2] showed interest in an old drill hole with a plug. Unfortunately not very good photographs.
Funny enough the wall is facing North which is a hint with regards to nesting behaviour I had recently read about and the preference for nests facing North or West  . I have started an experiment for this purpose with small nest blocks, see bee hotel sections V en VI.
References1 Nederlands Soortenregister
2 GUSENLEITNER, J. Bestimmungstabellen mittel-und südeuropäischer Eumeniden (Vespoidea, Hymenoptera) Teil 1: Die Gattung Leptochilus SAUSSURE 1852. na, 1993.
3 BUDRIENE, Anna. Reproductive ecology and behaviour of predatory wasps (Hymenoptera: Eumeninae). Doctor al thesis. Vilnius, 2004.