In Thugs' Warehouse - Inner Chamber fight stand over the trap door at the upper-right corner of the map and search it (5). You'll receive the unique Procurers' Cane (HP +10), a Soma and 51.
You can stand over the brown patch next to the well and use the button there to ignite the fountain (5 action points). The fires will damage anyone standing on the grey slab next to the fountain for up to 60 HP. The damage is one time only - after the ignition anyone can stand next to the flaming fountain without suffering any damage. Additionally, you can ignite the fountain only once (thus it might be better to save it for the slightly harder second Courtyard fight).
During the next fight once inside, you can topple over the bookcase to your right to deal 40 damage to a 2x3 area.
During the Boris' Mansion, Sitting Room battle you can cut the rope (5 action points) on the column nearest to you to drop the chandelier on a 3x3 area beneath it for up to 60 HP.
Episode 3 Edit
In every fight there are at least two confessionals or bookcases that you can bring down on the enemies, causing damage. In both fights in Church of Ecthain, Stairs map there are exactly two such bookcases, standing in a row (you need to stand at the side of the bookcase to tip it for 5, so here you need to first tip the left bookcase to reveal the tipping location of the right bookcase) on the top floor to reveal a hidden hole. Examine it (5) to get the Blessed Girdle (S. Attack +4), a Holy Beverage and 108.
Episode 4 Edit
During the Pagoya Hole fight look for the dripping gatormoose head in the upper left corner of the map. Stand on where the drops fall and examine (5) it. You'll receive Korova Milk and 100.
In the second Tierva Station fight, the train will arrive on the fourth turn, damaging everyone on the left track for 160-240 HP. You'll get a notification before its arrival.
The last secret is hidden in the garbage pile in Zofia's Fortress. When you examine it (5) you'll receive the Red Belt (+25% chance to counter melee attacks) and 25.