I tried to follow many of the guidelines stated in this article:

[https://entomologistlounge.wordpress.com/2017/09/18/insect-hotels-a-refuge-or-a-fad/](https://entomologistlounge.wordpress.com/2017/09/18/insect-hotels-a-refuge-or-a-fad/)

All the hole entrances are rounded to avoid damaging insect wings. Hole sizes and depths are appropriate for a variety of insects,  However, it's plastic, and natural materials would likely be better.

Update 2024/05/06: Added half-radius version for direct wall mounting.