Fun Atmosphere And Office Culture - Nobody Wants To Work In A Boring Office

Hey guys,
I'm from a small BPO (200 employees, multiple offices) and we are trying to redesign to build a fun working environment.
Everything from internal communication, environment graphics and posters, office activities, learning and development, etc.
We have grown from 0-200 and never had the opportunity to look at such things.
I'm sure this subject is also of interest to alot of other members.
I would be good if people could share which are the good things they like about their office or the things they have implemented or would like to see and have heard at other places.
Let your imagination run wild/ sky is the limit.
Cheers
Shitij

I'll start -
1. In my previous organization - we had a monthly office party in office where all employees including CEO had to come. Office updates, milestones, birthdays, anniversaries were celebrated.
2. A open house was held every month where 2 speakers would speak on any subject in the world. Once we had somebody talk about architecture and various philosophies behind it, it gives everybody a platform to speak, its off topic but still intellectually stimulating and its very good for team building.
3. Treasure hunts
4. Monthly team level outing
5. Annual Offsite for the whole company - all office all employees
6. Rewarding employee loyalty - generous gifts for 1 yr- 5 yr - 10 yr -20 yrs
7. Organized efforts for Festival celebrations