Please note that you must complete the Where’s my Brother? side quest before you can access the Lost Tower. As you explore Solino Valley in Baldo The Guardian Owls, you’ll come across Minisio on the same hill as the Sparagna puzzle for a Rune of Power.
He’s selling a map to the Lost Temple! To reach the Lost Temple, exit the map via the eastern map transition and proceed up the stairs. Look for a fallen log and walk across it to reach another raised hill. On this higher ground, you’ll find stairs leading down to a map transition. In this dark space, a robot slumbers. I’d avoid this guy as he’s a one hit wonder! Instead, work your way to the eastern side of this area to find a map transition to the Lost Temple!
Fumble your way through this dark area until you pass through an archway. Light the 2 braziers to light up the area you just came through. You can backtrack to see if you missed anything or continue on to the next area. Now this next area is huge, and I mean huge!! Head through the area, lighting braziers as you come across them. Eventually, in the northeastern section you’ll notice a line of braziers in a narrow path leading south. Follow them to find a guardian symbol with a pulsing sound alerting you to an owl tower. Play your horn then interact with the symbol on the pillar to your left to cause the owl tower to raise up.
Head inside to find Lapazza and a chest containing the Takame Shield missing item.