The Fortress of the Lone Serpent was larger than the Fume Cathedral, but that wasn't a valid comparison. Even though they were two Strongholds, the Fortress of the Lone Serpent had a much higher status, both because of its location and irregular energy.
Though Adam couldn't see the entire fortress from his perspective, but he could also see it from above from the fighter.
His mind immediately conjured up an apt comparison - with the Moon Colosseum, with all of it, not just the arena where he fought against Fromund.
The Fortress of the Lone Serpent was about the size of four of the Moon Colosseums, taking into account both the arena and the spectator seats along with the wide frame.
In other words, the site of the Fortress of the Lone Serpent could have been an entire neighborhood or small village from the Second Ring.
Step. Step. Step.
Adam entered the main courtyard, looking around at the complex structure of the fortress.