Real Madrid is a very tough team with a very good and sound reputation across Europe such that their football prowess is known across Europe and that can't be disputed but if you are to visit the bundesliga just like Madrid will be mentioned amongst the top teams in Spain (la Liga) so will Dortmund be mentioned amongst the top teams in the bundesliga and across Germany, before now, Dortmund has always been the second runner up after Bayern Munich so I think it's even erroneous to think Dortmund is that small probably because they weren't at their best in their domestic league this season but then I believe getting to this point in the champions league is a boost to their confidence and by next season they can do better.
Let's not be surprised if Dortmund eventually gets to be a stumbling block to the Spanish side and making it really difficult for them and possibly getting to take the trophy from them because they are definitely not going to just allow this opportunity to be given off to Madrid without a fight just that Madrid has got a relatively firm depth which is their advantage but for Dortmund they have gotten good strength around their defense with which they can put up good resistance against Madrid so I don't think underestimating them is a good idea.