Commercial rated pilot reported flying over a congested city area; too low; in violation of 91.119.

Narrative

Around XA:29 pm local time; I rented Aircraft X from FBO at ZZZ and departed to the southeast. Around XA:31 pm local time; I requested a tour around downtown ZZZ1 with ZZZ Approach on frequency 12X.X. Later; Approach gave me a squawk code and transferred me to ZZZ Tower on frequency 12X.XXY.Around XX:33 pm local time; ZZZ Tower told me to 'maintain VFR at below 1;500 feet.' Then; I headed to downtown ZZZ1 while descending. Knowing that ZZZ airspace is congested and busy; I descended to a low altitude in order to keep myself away from airline planes; inadvertently going below the minimum safe altitude. I heard multiple departing aircrafts on frequency that could develop into conflicts; so I descended further down to around 400 ft MSL. During the descent; I kept my eyes outside to avoid any obstructions and aircrafts. I never heard ATC calling me about my low altitude.Around XX:40 pm local time; I contacted ZZZ Tower to inform them that I had finished the tour and was departing to ZZZ2. ZZZ Tower then told me to squawk VFR and approved me to leave the frequency. I did not receive any pilot deviation or number to call.After I finished the flight and went back home; I looked at my track log and realized that I was low in altitude during the tour. I unintentionally flew low; with my primary goal being to keep safe. I reviewed CFR 91.119 regarding minimum safe altitudes; which states that over congested areas; aircraft must maintain an altitude of 1;000 feet above the highest obstacle within a horizontal radius of 2;000 feet.To correct this; I plan to schedule a ground lesson with a CFI about Class B operations; controlled flight into terrain; and minimum VFR altitudes over congested areas. I plan to take FAASafety Wings Program courses on Class B Airspace VFR Operations (ALC-480); Controlled Flight into Terrain - Never Say Never! (ALC-603); and LOBO Live! - Low and Fast: Is It Safe and Is It Legal? (ALC-548).This incident has been a valuable learning experience; emphasizing the importance of adhering to minimum safe altitudes. I will obey CFR 91.119 while taking ATC commands when conducting flights.