Severe Shellfish Allergy

My dietary restrictions aren't life threatening but still would derail my trip and potentially lingering problems with vertigo- I sympathize! And also applaud you for not letting it stop you from adventures!
I found the grocery stores in Germany's "bio" sections really helpful, with the color coded allergen system but since I was watching for gluten and dairy I am not sure shellfish was included. You could look that up online.
I can't count either, on asking the servers about potential cross contamination. (I take a big supply of protein bars and peanut butter pouches for those times I can't get the information.)
Some time online will likely help you find options that don't even serve shellfish at all. Vegetarian should be safe?
Safe travels!

Csalamon, I feel for you. Traveling with a food intolerance or allergy is difficult. I have Celiac Disease. While my symptoms aren't life-threatening, as yours are, I cannot risk ingesting gluten while traveling. I don't have specific suggestions for restaurants, but I will share what I do to prepare for our trips.

In the months leading to a trip, I get on Google Maps and look for restaurants in the cities we will be visiting. I then click on each restaurant's website and go to their menu. From the menu, I can see what they offer that I could eat and what will cause possible cross contamination such as frying onion rings in the same oil as french fries. I then make a list of restaurants for each city and save them on Google Maps. It literally takes days to do this and find a couple of restaurants in each city. Depending on how long we stay in each city, we may return to a particular restaurant a couple of times. I'm totally OK with eating the same thing a couple of times if I know it's safe.

I also use a couple of apps built for finding restaurants that have gluten-free food. Maybe there is such and app for shellfish allergies?

Some cities are particularly difficult. In those cities we frequent grocery stores for meals. Luckily, my husband is easy-going and is willing to do what I need to do in order to eat a safe meal.

Since a shellfish allergy is not as common as some other food allergies, I'm not sure how many replies you will get for specific restaurants. You may have to do the tedious work of looking up the menus for restaurants. From each menu, you should be able to see if they have any shellfish in their kitchen.

Good luck, and I wish you a safe trip. I know how hard it is to travel with a food intolerance/allergy!

Following on from slbdaisy's reply, you could look up restaurant menus online for restaurants in each place, and try to identify places without shellfish on the menus - time consuming I know.

Agree with slbdaisy and Lin C that you could spend time looking at online menus. Riding trains to your next destination is a great time to do this kind of research. Additionally, my observation of many traditional Austrian and German brewery restaurants I have visited is that shellfish is relatively uncommon. Beef, pork and chicken are the mainstays.

You have a better chance in Austria and Germany than Italy of being safe. One thing I will pass on, is to have some type of clear allergy warning card available. Restaurants throughout Europe tend to be very good about accommodating allergies, but sometimes things are lost in translation. While "Shellfish" is a general category, some places do distinguish between Mollusks (Oysters, clams, Mussels) and Crustaceans (Shrimp, Lobster) so have a more extensive list of items listed as examples. Of course Calamari, Octopus, and squid might be considered differently yet.

You have a better chance in Austria and Germany than Italy of being safe.

I second that. As Austria has no access to the sea shellfish is not so common in the local cuisine. If you avoid posh places or restaurants serving foreign cuisine you should be rather safe. Try typical local restaurants offering traditional Viennese cuisine.