What to do on Birthday

I dont have many friends my 2 best friends super busy on weekdays and my birthday come in weekday. I was always an introvert and liked alone times but last 3 years because of work colleague i become extroverted and i need atleast one person with me to hangout. Now i want to go back to the times i enjoyed alone. Will try to enjoy alone for my birthday any suggestion on what to do alone for enjoying or atleast relaxing and having a peaceful day?