We strongly recommend to arrange for your accommodation well ahead of the conference, since Pontresina and surroundings are a favourite tourist destination in the mountains (September is hiking season). We recommend to make use of the standard hotel and renting platforms to make early reservations at hotels or to rent an apartment, e.g. for groups. You can also stay at nearby villages which are typically well connected to Pontresina by public transport such a trains and buses. When staying at hotels, guests usually get a voucher to travel for free in the area.
