Charcoal, 239 238 bytes
ＵＲ¹⁶¦²²Ｐ×_¹⁶↘¹”“1T↘Ｈ‖⌕⦄Ｑ⌈⌀MH⁷鱫cＪε⎚#÷‖↧⸿ÿ_Ｍ±Gςθx↥<]˜t~⁻？Ｔ\`⪫F№⮌ξv‹⎇αδ¹9∨q¢←6X$⪫ＳＡ‹¤ü‖§Ｄ‹v⁸)⮌s？ＡNＨτ!‰ZＮσE⟲—>£'αlＴ↙№%Ｍü‴⟲@ιＲＱ$⟧.ηψf◧4\™¬‴χe@“σXＮ±Ｉ%T↧~w—A⁵6ζ▶‴À$“UX0⁰Ÿβ˜¤c⁷ＤFＱm→>H⟧∨^‹α~ok∨Ａ1ψς9œ⁸}'¶$β”Ｐ×_¹⁴Ｍ↓Ｐ×_¹⁵←_/↑²² Ｐ×_¹⁶Ｍ⁵¦²Ｐ↘⁸Ｍ¹⁹↓↗⁸‖Ｂ
Try it online! Link is to verbose version of code. Most of this is simply printing a large compressed string, but the repetitive parts have been coded separately to reduce the length of the string; in particular the Rectangle saves a number of bytes by avoiding the space padding to reach the 17th column and even the diagonal lines save a byte each.
Rectangle(16, 22); For the |s in the 2nd and 17th columns
Multiprint(Times("_", 16)); Overwrite the 2nd row with _s
Print(:DownRight, 1); Print the \ in row 2, column 2
Print(<compressed string>); Print the bulk of the web
Multiprint(Times("_" 14)) Print the _s in the penultimate row
Move(:Down);
Multiprint(Times("_" 15)); Overwrite the bottom row with _s
Print(:Left, "_/"); Print the / in the bottom row
Print(:Up, 22); Print the |s in the 1st column
Print(" ");
Multiprint(Times("_" 16)); Print the `_`s in the 1st row
Jump(5, 2);
Multiprint(:DownRight, 8); Print a long diagonal line
Move(19 :Down);
Print(:UpRight, 8); Print the other long diagonal line
ReflectButterfly(); Mirror the first 16 columns (17th is axis)
Edit: Charcoal no longer seems to recognise the compressed string, and its current compression generates a shorter string which saves 5251 bytes, and allows one of the diagonals lines to be moved back into the string for a further 32-byte saving. (Note that these aren't the counts displayed by -sl; indeed even the original count appears to have been off by 1.) However there are twothree additional savings that would also have applied to the original code: Try it online!
- 1 byte by using
Ｂ(Box) instead ofＵＲ(Rectangle). - 1 byte by using
↙Ｐ×_¹⁶←/instead of↓Ｐ×_¹⁵←_/. - 1 byte by using
×_¹⁶Ｊ⁵¦¹instead ofＰ×_¹⁶Ｍ⁵¦².