Responses
Have you tried the sequel of UGH that is ongoing?
http://www.mangago.zone/read-manga/under_grand_hotel_kiss_kill/
You can try "Deadlock" too. It has a few similarities. Not completely like UGH though.
http://www.mangago.zone/read-manga/deadlock/
And if you are really craving for some boys love stories that start from prison & are complete then you can try this -
http://www.mangago.zone/read-manga/aiso_tsukashi/
You can also try "Haku no Naka" if you don't mind bl novel -
http://9th-ave.blogspot.com/2013/04/novel-in-box-in-box-pt-1.html
Are there any other manga like Underground Grand Hotel?