Hennepin Island tunnel
...that the 1869 collapse of the 2,500-foot-long Hennepin Island tunnel resulted in cementing over the only major waterfall on the Mississippi River?
...that the 1869 collapse of the 2,500-foot-long <b id="mwEJo"><a class="mw-redirect" href="./Hennepin_Island_tunnel" id="mwEJs" rel="mw:WikiLink" title="Hennepin Island tunnel">Hennepin Island tunnel</a></b> (<i id="mwEJw">pictured</i>) resulted in cementing over the <a class="mw-redirect" href="./St._Anthony_Falls" id="mwEJ0" rel="mw:WikiLink" title="St. Anthony Falls">only major waterfall</a> on the <a href="./Mississippi_River" id="mwEJ4" rel="mw:WikiLink" title="Mississippi River">Mississippi River</a>?