You need a docker installation and a user/password at store.docker.com.
If you got this you can establish a sqlplus session with this docker command:
docker run -ti --rm store/oracle/database-instantclient:12.2.0.1 sqlplus "user/password@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(Host=your.host.site)(Port=yourport))(CONNECT_DATA=(SID=yoursid)))"
Keywords: docker, oracle, sqlplus, easy