I know we've been to Soon's gate and Dorukan's gate. What do we know about Liirian's gate?
Covered in the prequel book "Start of Darkness".
[sblock]
It was the first gate Redcloak & Xykon attacked. 3 Years before the OotS was founded as I recall.
Liirian defeated Xykon and Redcloak rather thoroughly. But she left them alive and imprisoned, and Xykon was stripped of all spellcasting by a magical disease she created through Epic Magic that permanently nullifies all spellcasting. Only her and her allies had the vaccine.
Redcloak was immune because the Crimson Mantle gave him artifact-level immunity to disease, enough to overcome the Epic spell. Since he didn't have any spells that could get them out of the sealed cavern they were imprisoned in, he came up with a plan to turn Xykon into a lich, so he'd be immune to diseases and get his spellcasting back. He used the herbs and fungi in the cavern as a makeshift lab, and used his holy symbol as the phylactery because it's all they really had to work with.
Once Xykon got his spellcasting back upon transformation, he blasted their way out of there, ambushed Liirian, Energy Drained her, then Soul Bound her into a gem so she couldn't be resurrected.
Unfortunately, in the resulting battle, the gate was burned down. They went to the Dungeon of Dorukan as a secondary target to seize a gate. Dorukan was defeated only because Xykon used the fact he'd killed Liirian as emotional/psychological warfare against him to taunt him into acting recklessly, as the two loved each other (and that little "summoning" hole in Cloister was apparently engineered so he could teleport her in periodically, not every member of the OotS was as serious about the "never check on each other" clause as Girard and Soon).
[/sblock]
The aftermath of the incident at Liirian's Gate, with Sapphire Guard members investigating, was seen very briefly as a flashback in Comic #290
Giant In the Playground Games