Cornerstone is the largest of the slaad cities. Its architectural style and precise layout are constantly changing, but it’s always a sprawling city that houses hundreds of thousands of slaadi. If Cornerstone is held by the Concordance of Iron, it has vast armies drilling (though their tactics and units constantly shift). If it’s under the influence of the Final Regency, there are immense temples and countless shrines to the slaadi interpretation of the Sovereigns. The Random Settlements tables of the Dungeon Master’s Guide can be useful here to determine specific attributes of the current incarnation.
The attitude of slaadi toward adventurers depends on the active culture. The Final Regency may welcome adventurers who profess devotion to the Sovereigns, provided they don’t question the Regency interpretation. The Confluence of Reality celebrates extraplanar visitors, desiring their stories and performances. Meanwhile, the Cornerstone of the Glorious Union of Flesh is a very dangerous place to visit! Regardless, Cornerstone is the best place to acquire Kythrian artifacts or magical services.