Leigh Brackett's sword & planet adventure The Sword of Rhiannon is a short novel but a favorite among aficionado's. It was first published Sea-Kings of Mars and Otherworldly Stories in "Thrilling Wonder" Magazine in 1949 (cover artist Earle Bergey).
This really is a gem. Written before Sci-Fi and Fantasy really became substantial genres of their own, the summary of this sounds Sci-Fi but really is Fantasy. The Mars milieu features little technology; in fact, it is almost exclusively populated with fantasy creatures ("halflings" that are like reminiscent of harpies, mermaids, and man-serpents) and fantasy/historic technology (swords, pirate ships); there is a lack of laser guns and air-ships. Actually, the technology that enables some interesting time/space travel is rooted in a Lovecraftian Mythos magic associated with an elder race (Quiro).
Our protagonist is Carse, an archaeologist/criminal who is very "Indiana Jones" like (of course this was created long before Indy Jones hit theaters). The titular Sword of Rhiannon is revealed from the start to Carse; it had been hidden for centuries in a tomb, so it was rumored, and he quickly finds the tomb from which it came as sought treasure to loot. His adventure begins as he comes into contact with eldritch forces...
The adventure is high throttle action from start to finish. The reader learns more of the curse of Rhiannon. However, there is a rich history and dynamics between cultures that are not fully realized. I would have enjoyed experiencing more of: the initial/future perspective on Rhiannon's past, the Dhuvian's oppression of others, the demonstration of Rhiannon's power(s), the demonstration of the Sword's power or purpose...
Brackett's prose is deeper and more poetic than one expects from pulpy Sword & Planet. Here is an excerpt:
"It was a long way to the city. Carse moved at a steady plodding pace. He did not try to find the easiest path but rammed his way through and over all obstacles, never deviating from the straight line that led to Jekkara. His cloak hampered him and he tore it off. His face was empty of all expression but sweat ran down his cheeks and mingled with the salt of tears.
He walked between two worlds. He went through valleys drowsing in the heat of the summer day, where leafy branches of strange trees raked his face and the juice of crushed grasses stained his sandals. Life, winged and furred and soft of foot, fled from him with a stir and a rustle. And yet he knew that he walked in a desert, where even the wind had forgotten the names of the dead for whom it mourned.
He crossed high ridges, where the sea lay before him and he could hear the boom of the surf on the beaches. And yet he saw only a vast dead plain, where the dust ran in little wavelets among the dry reefs. The truths of thirty years living are not easily forgotten."
This book is very well done but feels like four servings of a five-course-meal. It is a quick read and well worth it, but apparently this is a stand alone adventure. This novel could easily have been inflated to 2x its length without departing from its pulp-adventure roots (i.e., it would not become filler-saturated epic fantasy). Brackett did write more Sword and Planet, but not with Carse.