Culture is really positive - hierarchy (although there is one) doesn't really interfere with the ability to built meaningful work relationships. Not much socialising after hours.
There is a divide when it comes to socialising with partners but it is still quite casual and fun. My team have lunch together every day and coffee catch ups in the morning and afternoon which is a great break and a great way to get to know the team. My team itself are very friendly and do drinks every Thurs/Fri. They do not pressure you to go.
There are always going to be separate groups amongst each level of employee, however in audit we work in small teams across these levels together, so it feels that we are able to collaborate with everyone mostly equally. GT does a really good job of closing the gap between a base level employee such as myself and for example the partner. So in general, the culture is really good.
Opportunity to socialise during and outside of work with colleagues - sometimes its up to you to make the effort and organise events.