\documentclass[border=2pt]{standalone}
\usepackage[utf8]{inputenc} % this is needed for umlauts
\usepackage[ngerman]{babel} % this is needed for umlauts
\usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf
\usepackage[margin=2.5cm]{geometry} %layout

\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.13}

\begin{document}
\definecolor{c1}{HTML}{0072B2}
\definecolor{c2}{HTML}{009E73}
\definecolor{c3}{HTML}{CB0000}
\begin{tikzpicture}
\pgfplotsset{
    scale only axis,
    % scaled x ticks=base 10:3,
    xmin=0, xmax=171,
    width=15cm, height=8cm,     % size of the image
}
    \begin{axis}[
            axis y line*=left,
            ymin=0.15,
            % ymax=26000,
            grid = major,
            grid style={dashed, gray!30},
            ylabel=validation accuracy,
            legend style={at={(0.5,0.1)},anchor=south},
            % ylabel style={at={(0,1.0)}    },
            xlabel=epoch,
            % legend style={at={(0.3,0.2)}, anchor=north},
            % legend cell align=right,
            xticklabel style=
            {/pgf/number format/1000 sep=,rotate=60,anchor=east,font=\scriptsize},
         ]
          \addplot[thick, c1, mark=., densely dashed] table [x=epoch, y=max_acc, col sep=comma] {baseline_cifar_test_acc.csv};\label{plot_one}\addlegendentry{maximum validation accuracy}
          \addplot[thick, c2, mark=.] table [x=epoch,y=min_acc, col sep=comma] {baseline_cifar_test_acc.csv};\label{plot_two}\addlegendentry{minimum validation accuracy}
    \end{axis}
    \begin{axis}[
      axis y line*=right,
      axis x line=none,
      % xmin=0,
      % xmax=171,
      % ymin=0, ymax=100,
      ylabel=loss,
      legend style={at={(0.5,0.1)},anchor=south},
      y dir=reverse
    ]
          \addlegendimage{thick, c1, mark=., densely dashed}\addlegendentry{maximum validation accuracy}
          \addlegendimage{thick, c2, mark=.}\addlegendentry{minimum validation accuracy}
          \addplot[thick, c3, mark=., dotted] table [x=epoch,y=mean_loss, col sep=comma] {baseline_cifar_test_acc.csv};
          \addlegendentry{mean loss}
    \end{axis}
\end{tikzpicture}
\end{document}