Dollis Brook Viaduct
... that the Dollis Brook Viaduct is the highest point on both the Northern Line and the London Underground above ground level, reaching 60 feet (18 m) in height?
... that the <b id="mwB0M"><a href="./Dollis_Brook_Viaduct" id="mwB0Q" rel="mw:WikiLink" title="Dollis Brook Viaduct">Dollis Brook Viaduct</a></b> is the highest point on both the <a class="mw-redirect" href="./Northern_Line" id="mwB0U" rel="mw:WikiLink" title="Northern Line">Northern Line</a> and the <a href="./London_Underground" id="mwB0Y" rel="mw:WikiLink" title="London Underground">London Underground</a> above ground level, reaching <span about="#mwt20" data-mw='{"parts":[{"template":{"target":{"wt":"convert","href":"./Template:Convert"},"params":{"1":{"wt":"60"},"2":{"wt":"ft"},"3":{"wt":"m"}},"i":0}}]}' id="mwB0c" typeof="mw:Transclusion">60 feet (18</span><span about="#mwt20" typeof="mw:Entity"> </span><span about="#mwt20">m)</span> in height?