This quest can be obtained from Helen Turnbull in Cierzo. Helen is located on a wooden platform directly south of the Sea-Salt Inn. From the main entrance to Cierzo, turn south and you will see her waiting on the platform.
Speak with Helen and listen to what she has to say. After you’ve stated that you’re looking for work, Helen will request that you find a Mushroom Shield for her. The shield can be found in Blister Burrows, north east of Cierzo, as shown above.
Begin by taking the main road north east of Cierzo. Keep following the road as it turns north, until you come across a sign post which indicates the direction of Montcalm Bandit camp to the east. From here you will notice a wooden archway to the north, as seen in the image below. Follow the road under the archway until you reach the entrance to the burrow.
Before you enter the burrow, ensure that you have all necessary items equipped or in your pocket such as a light source, weapons, bandages, and healing potions. Leave your bag outside so that you can recover it later if you happen to fall in battle. You will encounter some troglodytes in the burrow which you will need to deal with before you can explore it properly.
The cave is easy to navigate and loops through a series of tunnels and chambers. If you are having trouble finding your way back to the entrance, just follow one particular path all the way until you descend down a slope to a main chamber. All the pathways through the tunnels lead to the main chamber, so you are bound to stumble into it.
You will note the difference when you’re in the main chamber as there is increased light from the structure of the chamber. The Mushroom Shield can be seen in the centre of it, as shown below.
Once you have the Mushroom Shield, head back up one of the slopes and follow the tunnels until you reach the Adventurer’s Corpse. The corpse is at the end of the tunnel which leads to the entrance, so following this will take you directly out. If you didn’t have enough space in your pockets to loot everything inside, go back in with your backpack and collect everything. You can then sell what is useless back in Cierzo.
Take the Mushroom Shield back to Helen Turnbull to complete the quest.