Music at CERN
Yes, there is a piano in the Main Auditorium, but it is reserved only for performances/concerts. If you are interested in organising such a performance, please contact the Staff Association (Staff.Association@cern.ch). If you would like to practice, you can contact the Jazz Club (Vice-President and Secretary Marc Vanden Eynden: Marc.Vanden.Eynden@cern.ch) which has two upright classical pianos, or the Learning classical music club (LCMC-info@cern.ch) which also has a piano.
Outside visitors
Yes, you should request a visitor's pass for each visitor. You can find more information here.
Unfortunately outside visitors cannot stay at the hostel. The rooms are exclusively for people working at CERN. However the hostel will be able to give you some addresses for hotels in the CERN/ Geneva area.There are also many hostels in Geneva centre, some of which have rooms / dormitories where one can stay for a few nights.
It is possible to take visitors on CERN site but you will have to request a visitor's pass for them systematically. You are responsible for them and you have to accompany them at all times.
They can come on site with the car, if they have a visitor's pass and you are with them and you show your ID card to the guards, explaining that they are your visitors.
Overtime
The CERN Staff Rules and Regulations exclude the possibility for students to do overtime, night work, Sunday work, standby duty, shift work, and you are therefore not entitled to compensatory pay or leave.
This does not imply that you can only work from Monday to Friday from 8.30 a.m. to 5.30 p.m. with a break of one hour. However, any additional worked hours may be compensated in agreement with your supervisor by time off during the appointment (and not at the end of the appointment).