Manure may be an excellent substrate for many of these mushrooms or truffles but yeah I can imagine you don't want to risk having
pieces of it still in there.
I'm in Holland and I agree with the above poster generally. Do your own research first by checking on different basics of truffles (aka sclerotia) like
different kinds and experiences. Also check dutch smartshop sites (which will not be named here!). Then with your own knowledge discuss and compare
this info with a smartshop owner. The truffles are (as were mushrooms) virtually always packed in 'single dose packs' but remember that if you have little
or no experience with this and if you are in a foreign country that the effect will impact you significantly harder.
I strongly recommend you don't go over 1/2 to 3/4 of a pack for your first time - 2/3 may be fine for example. Especially if you'll be walking through a busy city, that can easily be too intense. Visit a park like the Vondelpark in Amsterdam and stay there for at least the comeup and peak of the trip. Being in semi-nature will give you some sort of comfort and safety from an uncontrollable environment, at least more than walking in the inner city.
If you can visit the home of friends there a whole dose can be okay. Because you have a sort of HQ and privacy, on the other hand being outside especially in nature is much more interesting and adventurous.