In the present world, the southern seas.
It didn't take much time for Volos and Eros to cross the great distances; they traveled through the deep Spirit Realm, and within a few flashes, they shifted from the Spirit Realm to a position above the Sea Emperor's palace.
The fragrant sea, the nearly nonexistent guards, the faintly visible luxurious Divine Palace—that was all there was to it. Clearly, the Sea Emperor didn't believe anyone could silently approach him through the sea—of course, he wasn't actually wrong about that.
Just like now, even the 'black and white ocean' reflected by the first layer of the Spirit Realm looked different near Poseidon's domain, even containing some colors within it.