import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

def plot_3d_surface():
    # Create a grid of points
    x = np.linspace(-5, 5, 100)
    y = np.linspace(-5, 5, 100)
    x, y = np.meshgrid(x, y)

    # Create a function to define the surface
    z = np.sin(np.sqrt(x**2 + y**2)) * np.cos(x) * np.sin(y)

    # Plotting
    fig = plt.figure(figsize=(10, 8))
    ax = fig.add_subplot(111, projection='3d')
    ax.plot_surface(x, y, z, cmap='viridis', edgecolor='none')
    
    # Customize the plot
    ax.set_title('3D Surface with Hills and Valleys')
    ax.set_xlabel('X axis')
    ax.set_ylabel('Y axis')
    ax.set_zlabel('Z axis')
    
    plt.show()

# Call the function to plot
plot_3d_surface()