It's the end of the final story in Superman #176, "Superman's Day of Truth!" We learned that Superman and Supergirl spent the day being brutally honest in honor of a Kryptonian holidy. This celebration commemorated Val-Lor, who once stood up for freedom against Kryptonian invaders, even though he was killed for it. His honesty inspired a revolt that chased the occupying Vrangs from Krypton.
Aha! he informs them. That's the middle of the ocean, where he ONCE did indeed have a fortress. (This was in 1958's Action #244, "Superman's Undersea Kingdom.")
And so, our story comes to an end with the supporting cast understanding the reasons behind "Superman's Day of Truth!" Typically, the final panel depicts our noble hero departing while Lois and Lana *sigh* dreamily.
The bottom half is one of those typical "start a hobby" ads.
See you Monday for the final pages of this comic!