Tomb of someone important (5th edition dungeon crawl part 3)

Continued from here.

Oldbook visited several monasteries, looking for a cleric willing to follow him underground.
In one of them, bard managed to catch on the rumor he was looking for (poison + dead three) - the water in the well at the entrance chamber is poisoned, due to the vine blight living there.

After two days of asking around, he was introduced to Grom, young half-orc priest of war. Two man found common language through the half-breed origin, and Grom agreed to follow Oldbook and try to stop the undead menace.

In order to reach the room with a zombie, heroes could pass by the stone jaws trap in 1 or by the giant fire beetles in 4.
They decided to go for the beetles, having in mind that once the giant insects were killed, they will have clear path back.
4 beetles were not a big issue for the bard and cleric. Heroes collected their glands and stored them for future use.
Then, Oldbook opened the wooden door, and Grom stepped in, with crossbow at the ready. There was still one zombie in the room. Pair quickly reduced him to 1hp, but thanks to Undead Fortitude, zombie refused to stay down. After 4 or 5 hits, zombie finally failed constitution check and was gone.
Then, while they were tending each other wounds, Oldbook reminded Grom that he is a cleric, and that he can kill zombies with radiant damage, something half-orc forgot in the heat of the battle.

Heroes picked up one fire beetle gland  and dropped it down into hole. At the bottom, they could see the circular antechamber to the tomb, but more importantly, another zombie climbing up. Pair prepared for a battle, and this time zombie was down quickly, thanks to the cleric's sacred flame cantrip.

After noticing that antechamber is empty, Oldbook and Grom took a short rest before venturing forward.

1. Heroes descend into antechamber. This tomb belongs to someone important - it could be seen by the way the walls were decorated. A corridor was leading east, and there were wooden doors to the south.

2.  Stable for afterlife. The owner's horse was buried here. And it was still there, as warhorse skeleton. The heroes didn't want to feel these hooves on their skin, so they retreated back into antechamber.

3. Big rectangle chamber behind the wooden door seemed empty, until another zombie guardian crawled out of the shadows. But single zombie was not a mach for cleric and bard. After killing the zombie, Oldbook wanted to leave, but Grom followed inscriptions on the wall and detected secret door. It was locked, and the pair had no means to open it. It was maybe better for all, since if the horse was too much for our heroes, meeting its owner would be certain doom for them.
Suddenly bard understood that the advice he received earlier was connected with this secret door. To open it, he will have to take the risk with the monsters in the mountains. But that seemed like a far future at that moment.

Discussing this, our heroes returned to the surface.

To be continued.