This elegant apparation was stretching on and around the bee hotel. It is an ichneumon wasp female of Ephialtes manifestator.
This wasp has a more than impressive ovipositor that she was cleaning intensively, striking poses like a gymnast on the beam. The pictures show clearly that the ovipositor is kept in a shaft that consists of two parts that can be zipped together. The shaft is flexible and can be bend controllably, wheras the shaft is stiff and inflexible what gives the wasp a challenge when trying to position it in a bee nest opening. This pdf on bijenhotels.nl provides and excellent overview how the wasp uses her ovipositor and the headaches it provides at times.
The wasp is a parasite on among others Red mason bee (Osmia bicornis), Chelostoma florisomne, Chelostoma rapunculi and Heriades truncorum. I’m sure the first and the last bee families nest in the bee hotel, the others may still be in photo backlog awaiting identification.
On this observation from 2015 it is clear how the wasp can get to her target.
Looking at the diameter of the bamboo rod it is probably a nest of Ridge-Saddled Carpenter Bee (Heriades truncorum) that is being infiltrated.