The workshop will be held at the Tallink Spa Hotel (Tallinn, Estonia) on May 19 (afternoon) and May 20 (full day). The workshop is held right after the EUROCRYPT 2011 conference. This hotel a 15-minute walk away from the Eurocrypt 2011 venue (Sokos Hotel Viru). Note that there are several Tallink hotels. (In fact, Tallink City Hotel is just next to Viru Hotel, but this is not the correct hotel.) Hash-2011 participants who also attend EUROCRYPT 2011 will be guided to the Tallink Spa Hotel by the workshop organizers.
More practical information can be found at the web site of EUROCRYPT 2011.