Kim Kardashian Spent Her Birthday…at a Museum?

Reality star decides to keep her celebratory shenanigans mellow. Well, for today, anyway

Being a married woman in her 30s has definitely influenced a more mature birthday outing for Kim Kardashian.

Granted, the reality star will still be doing her usual birthday bash in Vegas this weekend at Marquee nightclub, but today (her actual date of birth) the newlywed spent her 31st with sis Kourtney Kardashian and nephew Mason (and a gorge turquoise Chanel bag) at the Natural History Museum!

"Good morning dolls! Last day in New York! Off to Las Vegas tomorrow! Can't wait!" she tweeted.

As you would expect, K.K.'s Twitter has been blowing up with birthday wishes today from fans, friends and family.

"Happy Birthday to my favorite Sister of the day @KimKardashian! Let's boogie!," brother Rob Kardashian tweeted, along with friend and wedding attendee, Eva Longoria saying, "Happy Birthday beautiful @kimkardashian Love U!"

Kim even scored a celebratory tweet from her much younger admirer, Justin Bieber.

Aw, cute!