The Caspian Sea is the lowest point in Europe. The Caspian sea divides Europe from Asia and not all countries that have a boundary with the Caspian Sea are in Europe. Therefore it is not sufficient to visit the shoreline of the Caspian Sea to claim reaching the low point of Europe, it is also important to be in Europe at the same time. This is where the definition of Europe becomes quite important.
The modern boundary of Europe includes the Caspian Sea to the North of the Caucasus watershed in Azerbijan continuing clockwise to the Ural Mountains in Kazakhstan. And includes the entire Russian Federation boundary with the Caspian Sea. Large parts of the Azerbaijan and Kazakhstan boundary with the Caspian Sea as well as all of the Iran and Turkmenistan boundary are in Asia.
The following shows the modern boundaries for Europe and Asia. Green represents States geographically in Europe. Light Blue represents Transcontinental States in Europe, Dark Blue represents Transcontinental in Asia and Purple represents States geographically in Asia. There is a small part of Egypt that is also considered part of Asia.