I've found the office's very comfortable. The set ups at the desks allow for some adjustments to suits an individual's physical needs. There are a several different office's located around Canberra (and the also some in the States). The facilities are also to a good standard. The dress code varies throughout the Department as different Sections have different dress codes. Usual business attire is the most standard (e.g. long black pants, collared shirt, no ties).
The main DSS building is located in Tuggeranong which is the deep south of Canberra. It is VERY different from working in a city environment. Sitting in the work "cafe" which is full of couches and has dart boards etc.. you stare out onto towards the bush and the mountains and it can feel like you're actually at a country retreat as opposed to work! The dress code is business attire, but there is no expectation for the kind of corporate dressing you might be used to seeing in the cities.
DSS National Office is located in Tuggeranong Office Park. The location is approximately 20 minutes south of the centre of Canberra. A new office building is scheduled to commence work in 2015.