Deuteronomy 27:8 as explained by Rashi says that the Torah was written in seventy languages on stones. What happened to the stones? These would have been big stones. Are there any hints as to where they went?
The verses right before this (27:2–4) explain that when they crossed the Jordan they took along with them big stones. The gemoroh (Babylonian Talmud) in Sotah bottom of 32a says they took (those –Rashi) stones and built the altar and inscribed in it the torah in seventy languages; brought a few korbonos, then dismantled the altar and went to Gilgal, taking the stones with them. Rashi on the top 32b says they made a monument out of the stones in Gilgal.
So to answer your question: According to Rashi they were made into a monument in Gilgal.
The previous answer (from @skraz13) is complete in terms of explaining where these stones were initially established by Yehoshua and B'nai Isra'el.
For what it's worth, see this article which says (excerpts):
Israeli papers are reporting the discovery of an underground quarry in the Jordan Valley. Prof. Adam Zertal and a team of archaeologists from the University of Haifa are working on the hypothesis that this is the site of biblical Gilgal.
The large cave was discovered by Prof. Adam Zertal and a team from the University of Haifa which has been conducting a survey of the region since 1978. “When we reached the entrance to the cave, two Bedouin approached us and warned us not to go in, because it was cursed and inhabited by wolves and hyenas,” Zertal said yesterday from the site.
They entered anyway, discovering a ceiling supported by 22 gigantic columns on which various symbols were carved, including 31 crosses, a possible wheel of the Zodiac and a Roman legionary symbol. The columns also had niches for the placement of oil lamps and holes that apparently served as hitching posts.
Potsherds found in the cave and the carvings on the columns led Zertal to date the first quarrying of the cave to around the beginning of the Common Era. It was used mainly as a quarry for 400 to 500 years, “but other finds give the impression it was used for other purposes, perhaps a monastery or even a hiding place,” Zertal said.
Zertal said scholars wondered why people would dig a quarry underground considering the effort needed just to pull the stones out of the ground.
A possible answer may be in the famous Madaba Map of ancient Palestine, found in Jordan. In it, a place named Galgala is marked and an accompanying Greek word meaning “12 stones.” The map also depicts a church near the site. Archaeologists say they have found two ancient churches near the cave.
According to Zertal, scholars had always assumed that “12 stones” referred to the biblical story of the 12 stones the Israelites set up at Gilgal after they crossed the Jordan. However, the discovery of the quarried cave may mean the reference was to a quarry established where the Byzantines identified Gilgal. Zertal explains that in antiquity sanctuaries were built out of stones from sacred places.
The inscription reads “Galgala, also the twelve stones.” Below the inscription is a small church with its entrance hidden by a long structure with 12 white spots on it (two rows of six). The Madaba map is dated to about A.D. 560 to 565
I can't access some of the links and images on this web page, and, in any case, the article suggests a possibility, rather than anything definitive. As I stated at the beginning, "for what it's worth". Proving or disproving Torah archeology is a difficult process to say the least.