What are some cities where touristy areas are located very near sketchy areas?

Self-explanatory title but basically, what are some cities where it's quite easy for an unsuspecting tourist to go from a tourist area and then accidentally wander into a sketchy neighbourhood?

Based on my experience, the first two cities that come to mind are San Francisco and Barcelona. In SF, it's very easy for tourists to go from popular places like Union Square, Civic Center, and Chinatown into areas like the Tenderloin, which has become an infamous neighbourhood in the city for all the wrong reasons. And in Barcelona, it's very easy for tourists to go from touristy zones like Montjuic, Poble-Sec, and La Rambla/Gothic Quarter and then unknowingly entering into El Raval which isn't exactly the nicest area in the city by any means.

On the flip side, cities like London, Paris and NYC are generally very safe for tourists as the sketchy zones in those three cities are often located in the outskirts of the city and very far away from the crowded tourist spots, hence making it pretty much impossible for an unsuspecting tourist to accidentally end up there.

What are some other cities you've been to where this is the case? I think this would be good to know for all tourists alike who are looking to visit new cities they aren't familiar with